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ldavi_j

Extremely Rough Idling, Stalling, And Rpms Falling To Near Zero

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I have a 2000 Mazda 626, and it has 186,000 miles on it. I bought it from my sister roughly 2.5 years ago, and the car's had idle problems practically since I got it.

Back in the summer of 2011, the idling had gotten so bad that my car would stall in traffic, at stop signs, stop lights, drive thrus, in park etc. I took it to a shop to have it tuned up and explore other possible problems, and I was informed that my spark plugs were bad and that's what was causing the stalling. After they'd replaced the spark plugs, the mechanics told me that my idler was bad and that my car would still idle but not stall out. I'm not sure if they meant my IAC valve or IAC motor was bad.

In the past few months, my car's idling problems have progressed to where during times where my car idles, my RPMs fall way below 1000 and close to zero. My car shakes and sputters extremely roughly until it dies (this usually happens when I'm in park or idling for longer than a few minutes -- otherwise, it just shakes and sputters), unless I press my foot on the accelerator a bit. If my RPMs are up, my car is fine. It's just when I idle that it is so terribly awful. Also, for example, if I've been in park with my foot on the accelerator to keep the car from dying, the car stalls as soon as I take my foot off the gas to switch into reverse or drive. I do keep my foot on the accelerator whilst in park at places like the bank or otherwise stopped and in park for an period of time for longer than a minute or two. Sometimes, my car won't stall after I take my foot off the accelerator after being in park, but it still shakes and sputters as if it's about to die.

Yesterday, my car died twice in traffic -- once at a stop light and the other time at a stop sign. A friend told me that my idle air control valve was probably on the fritz, so I ordered the part from AutoZone. Before I open the box and render the part unable to return, I figured I'd get some feedback from you all here on the 626 site.

I'm becoming increasingly annoyed and am very ready for this problem to be fixed. The reason I didn't get it fixed before now is that I simply haven't had the money, and I'm ready now to just get it over with. I appreciate all feedback and suggestions I may get! Thank you.

PS. I'm more than willing to answer anymore questions about the car if it can help narrow down possibilities. Also, I know next to nothing about cars. Forgive me if I seem ridiculous.

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In your case you'll need someone's help for this. With the car at 750-800 rpm unplug the connector to the IAC. Does the rpm want to drop on it own or make the car stall when unplugged? If yes the IAC is working, if no the IAC needs to be replaced. There are many other things that can affect idle speed and the list is so long that it would take me 5 minutes to write it out. Get your timing checked? The belt tensioner spring or "idler" pulley going bad could give you issues like this. There would be other noises associated with that most likely such as a high pitch whine coming from the timing belt area. If he meant a bad idler pulley and not IAC then you've just purchased the wrong thing and will want to return the IAC. Do the test above first though that should aid you in self-diagnosis.

Welcome to Mazda626.net klavi_j. :)

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In your case you'll need someone's help for this. With the car at 750-800 rpm unplug the connector to the IAC. Does the rpm want to drop on it own or make the car stall when unplugged? If yes the IAC is working, if no the IAC needs to be replaced. There are many other things that can affect idle speed and the list is so long that it would take me 5 minutes to write it out. Get your timing checked? The belt tensioner spring or "idler" pulley going bad could give you issues like this. There would be other noises associated with that most likely such as a high pitch whine coming from the timing belt area. If he meant a bad idler pulley and not IAC then you've just purchased the wrong thing and will want to return the IAC. Do the test above first though that should aid you in self-diagnosis.

Welcome to Mazda626.net klavi_j. :)

Okay, probably going to sound silly asking this, but... do you mean unplug the connector to the IAC motor or IAC valve? As I put in the question, I don't know really anything about cars, but I'll have my friend look at it tomorrow. Also, when you say the IAC may need to be replaced, do you mean the motor or valve? Redundant question, I know. Just want to make sure so I don't do anything wrong! :)

Do you know what kind of problems would indicate bad timing? This whole thing makes me want to pull my hair out haha.

And thanks!

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Before you just blindly replace parts based on a hunch or a likelihood, make sure that the old part in fact needs replacing.

The very very first thing I'd check is for air leaks. The symptoms you describe are classic for a bad air leak. Besides, inspection of an air leak is free and you can do it by yourself.

You'll want to make a very close visual inspection of all the air ducting leading up to, and including, the throttle body, as well as the intake manifold gasket (the gasket which seals the space between the intake manifold and the engine head).

You see, all the air which is ducted in to the engine passes through the MAF or VAF sensor (depending on which 626). This sensor measures the amount of air that is coming in through the intake. The computer uses this data, coupled with the data from the air temperature sensor, to tell the fuel injectors exactly how much fuel to spray into the cylinders, to provide the optimum combustion. Now, if there's an air leak downstream of the MAF/VAF (downstream meaning the section of air intake ductwork past the MAF/VAF sensor) then the amount of air that is actually arriving in the engine is being matched to the wrong amount of fuel. This causes terrible idle and sometimes decreased performance during acceleration, etc.

Go through and look at it all very closely. Also, take a can of throttle body & carby cleaner. Start spraying it around between the joins in the ductwork while the engine is running. If you hear the engine rev up for a quick second, that means some of the solvent from that spray can got into the ductwork through a leak or crack. Also spray it around the manifold gasket and other gaskets (throttle body, etc.).

Some other possibilities are a dirty MAF sensor wire. If dirt gets on the wire then it will report incorrect values of air mass or flow to the computer. Be extremely careful with MAF wires. They are extremely delicate. There's also the possibility of a broken MAF.

Also, perhaps your throttle body needs a good cleaning. Carbon deposits will build up inside the throttle body, mostly behind the butterfly valve. The amount that valve is open or closed regulates your throttle. The IAC motor actuates that butterfly valve to be open the perfect amount to allow the right idle speed. If the valve gets dirty and sooty/sticky, especially around the swivel pins on the sides, then the IAC has a very hard time actuating the valve properly. Often, a good clean of the throttle body and valve will do wonders!

Again, these are all tests and maintenance that can be done for the price of a can of throttle body cleaner.

Do the cheap and easy stuff before you start just replacing parts.

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Well I honestly didn't know there would be 2 connectors on the 5th gen IAC. On mine there's only 1. I would unplug both at the same time if possible.

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Before you just blindly replace parts based on a hunch or a likelihood, make sure that the old part in fact needs replacing.

The very very first thing I'd check is for air leaks. The symptoms you describe are classic for a bad air leak. Besides, inspection of an air leak is free and you can do it by yourself.

You'll want to make a very close visual inspection of all the air ducting leading up to, and including, the throttle body, as well as the intake manifold gasket (the gasket which seals the space between the intake manifold and the engine head).

You see, all the air which is ducted in to the engine passes through the MAF or VAF sensor (depending on which 626). This sensor measures the amount of air that is coming in through the intake. The computer uses this data, coupled with the data from the air temperature sensor, to tell the fuel injectors exactly how much fuel to spray into the cylinders, to provide the optimum combustion. Now, if there's an air leak downstream of the MAF/VAF (downstream meaning the section of air intake ductwork past the MAF/VAF sensor) then the amount of air that is actually arriving in the engine is being matched to the wrong amount of fuel. This causes terrible idle and sometimes decreased performance during acceleration, etc.

Go through and look at it all very closely. Also, take a can of throttle body & carby cleaner. Start spraying it around between the joins in the ductwork while the engine is running. If you hear the engine rev up for a quick second, that means some of the solvent from that spray can got into the ductwork through a leak or crack. Also spray it around the manifold gasket and other gaskets (throttle body, etc.).

Some other possibilities are a dirty MAF sensor wire. If dirt gets on the wire then it will report incorrect values of air mass or flow to the computer. Be extremely careful with MAF wires. They are extremely delicate. There's also the possibility of a broken MAF.

Also, perhaps your throttle body needs a good cleaning. Carbon deposits will build up inside the throttle body, mostly behind the butterfly valve. The amount that valve is open or closed regulates your throttle. The IAC motor actuates that butterfly valve to be open the perfect amount to allow the right idle speed. If the valve gets dirty and sooty/sticky, especially around the swivel pins on the sides, then the IAC has a very hard time actuating the valve properly. Often, a good clean of the throttle body and valve will do wonders!

Again, these are all tests and maintenance that can be done for the price of a can of throttle body cleaner.

Do the cheap and easy stuff before you start just replacing parts.

Right. I bought the part basically out of a fit of rage, which I now see was an ill-made decision. I can return it though.

I'll look up all these parts you've mentioned (I have no knowledge of cars) and try to figure out what's going on. A friend of mine is going to look at it tomorrow for me (his Jeep was doing literally the exact same thing and replacing his IAC motor fixed the problem) and let me know what he thinks it is. I'm kind of ashamed of myself right now for not knowing the innards of my car! Ha.

Thank you so much for taking the time to give a detailed explanation. I really do appreciate it! Cars aren't really my area of expertise, as you can tell.

So what do I do if there is an air leak? Also, is there a way of knowing for sure which hose is leaking? Then, if it is the hose, do I just take it to a mechanic and have him or her replace the hose? Sorry for all the questions!

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Get a length of hose. Old cut garden hose works great. Use it as a stethoscope you'll be amazed at what you can hear. You want to hone in on something that sounds like a hiss. Imagine an air tank in a movie that is releasing a lot of air or like an air hose blow gun if you know what that sounds like. Don't worry about not knowing your car. We've all been there.

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If there's an air leak in a hose or rubber boot or whatever, you're in luck. You know for sure which hose is leaking because you see a crack in it. Or for sure which hose connection is leaking because the engine will always spike up whenever you spray solvent on the connection. You just order the new hose/ducting and replace it yourself. It'll be like two clamps or something else fairly simple.

If it's a blown gasket then you might want to pay to have that done. You can definitely replace it yourself, depending on how handy you are, how patient you are and what kinds of tools and time you have.

You can clean the MAF yourself but read up on it and watch vids of it. I think Devon has one. You just need to be VERY careful with that wire. If it's a broken MAF, you can replace that yourself or pay to have it done. Replacing it is pretty straightforward. But they're pretty expensive for a new one so make sure first. In my experience, those don't break too often.

Cleaning the throttle body is always a good place to start because you need to remove all the air ducting to get to the throttle body. Removing the ducting is always a great time to check for visual cracks and separations, as you get a view all around each part as you remove it. You can definitely do a basic clean of the throttle body yourself. All you need is a can of cleaner and an old toothbrush and/or rag. There's tons of vids on it. A full clean requires removing the entire throttle body but you can definitely give the butterfly valve a good clean without removing the throttle body. If it turns out the throttle body gasket is your leak, then you need to remove the throttle body anyway. You would take that opportunity to give the whole thing a good clean.

Don't feel ashamed about not knowing everything about your car's internals. No one can know everything about everything and everyone has their own interests, hobbies and areas of expertise.

Of you have questions, we're always here to help.

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+1 what Devon said about listening. Can't believe I forgot to mention that! Hissing noises are a dead giveaway for an air leak. Listen closely all around whole the engine is idling.

Also, I've seen some people blow cigarette or cigar smoke through the air ducting to see if the smoke comes out of a crack or split. Never done that myself.

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Also, I've seen some people blow cigarette or cigar smoke through the air ducting to see if the smoke comes out of a crack or split. Never done that myself.

That method is done with the car not running by the way. :)

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All righty. I'm going to buy some throttle body and carby cleaner today after my classes are over. Which do I spray around while the car is idling to check for air leaks? Also, is it okay to spray those things if the engine is hot? I didn't know if fhat was potentially dangerous. I'm going to take a picture of my engine this afternoon and I'll post it here in case you all would like to see it. :) it is a total mess though. I might take a video to display how utterly ridiculously my car idles. I'll show how the RPMs and engine idle. When I first crank my car, my RPMs go up to 2 or so and then they fall down close to zero. I'll make sure that's also in the video.

Thank you again for the help! I'll definitely listen for the hissing and try unplugging the IAC connector as Devon suggested to see if my IAC is working properly. Will check back around 12 my time! It's 9:40am right now, so it'll be a little bit of a wait before I can get a picture up.

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Throttle body & carby cleaner is a single thing. It's not two separate products. Carburettors are what were used back in the days before fuel injection systems. Instead of having a MAF sensor measure the air flow and send that data to the computer and have a throttle body to control the throttle/idle and have fuel injectors for the computer to be able to control fuel flow with, there used to be a carburettor which was a fully mechanical, non-computerised version of device to accomplish the same job. It required periodical tuning and had to be adjusted for different conditions, where the temperature and density of the air outside was drastically different from location to location. Nowadays the computer has sensors for everything and can control everything on the fly, accordingly. The cleaner used to be called carby cleaner. Now it's called throttle body and carby cleaner. Honestly, I think it's just acetone in a spray can. I think.

Technically it's ok to spray while the engine is hot. But if I were you I'd let it cool down first, if only so you can reach the carby cleaner into nooks and crannys without burning yourself on anything. If you're not familiar around an engine bay and so don't know what to expect, just treat everything as if it were hot.

Another thing which could be causing your funky idle is an ECT sensor, or Engine Coolant Temperature sensor. That's off in a completely different direction. So let's try the air leak thing first. Hopefully that's it.

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Actually they are 2 separate products at least in name here in the US. You can buy a can called Carb Cleaner and a can called Throttle Body Cleaner. Same thing just 2 different names. MAF cleaner is about the same stuff too but it's less caustic and sensor safe (alcohol for faster dissipation). I believe they are all acetone based. Yes if you use that please have a fire extinguisher handy. It is possible for it to blow the intake manifold out it's not the ideal solution and definitely only use it on a cold engine. Let the engine cool down for a long time before attempting it because you don't want it igniting inside the intake manifold. Doing it while the engine is cold will give you the best chance for success and lessen the risk of an explosion or fire. It's better to use propane because it has a higher flash point than carb cleaner.

I agree with Roritor about checking the ECT but more importantly make sure you don't have air in your coolant system. If possible burp the air from the system (do a forum search on how to do this if you aren't sure). Most likely it's just an air leak but there's always the possibility of air in the cooling system which has almost identical symptoms during idle. An air leak would be much more pronounced at speed as you would notice lag between the time you stepped on the gas and the time you actually started to go.. the lag is about 2-3 seconds.

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I always see it as throttle body & carby cleaner. If they're selling it as two separate products it's because they want you to buy it twice.

Also true that MAF cleaner is a separate solvent, more gentle. I think it's alcohol based, yes. Like electrical contact cleaner. But they are not all alcohol based, as acetone is not alcohol. ;-) Alcohol is methane/methanol (wood alcohol, often used as fuel, present in flatulence), ethane/ethanol (the kind you drink) and isopropyl/isopropanol (rubbing alcohol). As far as using propane, acetone is actually far more similar to propane than alcohol. Another name for it is actually propanone and it is made from a substance called propylene. Anyway, enough chemistry! Have an extinguisher handy, have the engine cold, you really should be fine.

Devon, you're absolutely right about spraying it on a cold engine. It's definitely safer, come to think of it. I always just do it on a cold engine cuz that's when the idle is roughest anyway, and I won't burn myself on anything.

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The middle part of my idle air control motor came out. Pretty sure that's not supposed to happen. It like, just fell out.

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Okay, so I'm just really confused. There are two separate pieces, right? The IAC motor and the IAC valve. Those are not one in the same, correct? This has been my impression. I think I just don't know where anything in my car is.

Blah. I'm going to include some pictures:

http://imgur.com/ipJohkY --- What his screwdriver is on is the idle air control motor, right? If not, where is it? Also, where's the valve even at?

http://imgur.com/WWoY4xh --- This looks really bad. Gonna order a new one of these because it's practically dry rotted.

http://imgur.com/HkIWe8B --- My stuff. Someone please explain where everything is. :( I thought I knew, but then I started looking online for the IAC motor, and the results didn't match what I thought was the IAC motor (like in the first link). I just want to make sure I buy a compatible part.

Anyway, the throttle body gasket is in very bad shape. I bought a new one and will have it installed ASAP.

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The flex/hose that's taped is after the airbox and wont cause trouble per say. The tb gasket can. Also check the intake elbow ( from tb to maf ) for cracks ect while your at it. If your comfortable enough clean the tb while you have it off to replace gasket. here are some links that may help -

1.http://www.mx6db.co.uk/?loc=4&id=6&view=guide

2. http://mazda626.net/topic/25028-iac-valve-cleaning/#entry222152

3.Bear in mind the 626/MX6/Probe share the same drive train - http://forums.probetalk.com/showthread.php?t=1701257895

4.post #4 - http://www.mx6.com/forums/2g-mx6-general/234663-reving-problems.html

5.Good read/explanation -http://www.performanceprobe.com/forum/showthread.php?t=2907

I'm not sure if any of these will help but it is a good read and may help familiarize you with these cars a bit more.

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I forgot to add your IAC may look a bit different but they are all basically the same internally and share the same characteristics.

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Just to clairify:

1) 5th generation 626 models ('98-2002) have same IAC valve units (..this may not be true of the earlier generations).

2)The IAC valve unit has two 'halves' (...neither one is a 'motor');

the electrical plug half (First half) holds the 'plunger-like' valve and is operated by a type of 'electro-magnetic' process that

pushes the 'plunger' into the (Second half) other 'half' of the unit This second half is attached to the TB (throttle body).

Your initial idle problem is related to the EGR (Emission Gas Recirculation) system where vacuum plays a major part. If you have a vacuum leak in the system or a faulty 'valve/solenoid' sensor part then your operation of the car (..and the idle) will be affected.

That is what you will now have to do...find the problem(s) area.

A) It could be a bad gasket(s) or cracked hose(s) for the vacuum leak(s) and/or....

B) faulty/bad sensor/solenoid or IAC valve

Here is my first suggestion: Try cleaning your IAC valve...the 'plunger' half.(See above 'How-To' link.)

BTW- Test for vacuum leaks. The leaks will be after the air filter box connection to the MAF sensor unit then along the 'elbow' bellow then to the TB (Throttle Body) unit then to the IM (Intake Manifold) then to the motor. There are more smaller vacuum hoses that are attached to the IM and sensors/solenoids.

Good luck!

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When you say that your throttle body gasket is crumbled to pieces, did you mean that black rubber accordion bit that is all duct taped? Because that's not the throttle body gasket. Not even close. In fact, as Tjvr said, that accordion piece won't even affect the idle. This is because that piece is part of the "upstream" air ductwork. Part of the MAF is visible externally as that flat, black plastic piece that lives on top of the hose piece immediately after the big air filter box/housing.

IAC-MAF1a.jpg

So basically, any cracks in the ductwork before or upstream of the MAF, while not ideal, certainly won't cause a screw up in the air:fuel ratio and produce a poor idle. It is only cracks in the ductwork after or upstream of the MAF which will cause this issue. This is because, once the air has passed through the MAF, that is then the mass of air flow that the computer is adjusting fuel flow for.

78543418.gif

The throttle body gasket will not really be visible without actually pulling the throttle body apart. Yes, you can see the very thin, outer edge of it but that's it. That's why I recommended visually inspecting hoses and ductwork, and using carby cleaner to test for leaks on the gaskets (mostly the throttle body gasket and the intake manifold gasket). If you can get the engine to rev up when you spray on a gasket, then that's reason to pull the hardware apart, at which point you'll be able to see the actual gasket.

If you already knew all this, and I misunderstood what you were saying because of the way I perceived your pictures, well then I apologise.

If you have pulled apart the throttle body and you do have a trashed gasket, well that's almost undoubtedly your cause of your issue. And definitely while you're in there, as I mentioned before and as 98LazerRed said, give the whole throttle body and plunger/IAC a good clean.

If you havent yet actually pulled apart the throttle body, then just give the butterfly valve a really good clean with some carby cleaner and a toothbrush, on both sides of the valve. You'll need to hold the valve open against the spring the get to the underside. It's the underside that'll have all the soot, anyway. It's very likely that the outside face of the valve will look really clean as is.

That's the throttle body by the way:

Invisible-throttle-body.jpg

err...on the 626 it looks like this:

img-318775-1-ThrottleBody_Before.jpg

In the pic above, the throttle body has actually been pulled apart and we're looking at the butterfly valve from behind. That's actually the inside of the throttle body. Do you see all the sections of metal walls that separate all the different chambers? The gasket lays in between that throttle body piece and the piece it connects to. The gasket lives sandwiched in between, specifically on those metal walls, on the face of them directly facing us, as we look at the picture. It stops leaks getting passed the walls in the areas where the two halves come together. So to see the actual state of the gasket, you literally have to pull it apart. Unless it's so so bad that you can see missing chunks from the outside.

And I seriously recommend you check out this thread by DjDevon3. He thoroughly, and I mean thoroughly, details the assembly, disassembly, cleaning, everything of the throttle body and IAC, with vids and all.

So once again, you're visually inspecting for cracks and stuff on all the black, plastic ductwork downstream of the MAF. On the big black rubber/plastic elbow between the air filter box and the throttle body. On all the joins between the ductwork. And then spray some solvent around where the throttle body and intake manifold gaskets are.

And again, the issue may not even be vacuum leak related. As mentioned in an above post, it could be EGR related or coolant related. But I just want you to knock out one possibility at a time and I reckon air leak is simply the most likely, as well as easiest place to start.

Lastly, have you had your car scanned for error codes?? AutoZone will do it for free...that might stop us chasing our tails...

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The 5th gen IAC is completely different from the 4th gen. 5th gen owners can transfer over the general cleaning procedure but other than that the parts are too different. 5th gen owners should really read MazRedMan's 5th gen IAC Cleaning Tutorial instead as 98LazerRed suggested above.

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Oh. Yeah. Good call. :-)

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Just to clairify:

1) 5th generation 626 models ('98-2002) have same IAC valve units (..this may not be true of the earlier generations).

2)The IAC valve unit has two 'halves' (...neither one is a 'motor');

the electrical plug half (First half) holds the 'plunger-like' valve and is operated by a type of 'electro-magnetic' process that

pushes the 'plunger' into the (Second half) other 'half' of the unit This second half is attached to the TB (throttle body).

Your initial idle problem is related to the EGR (Emission Gas Recirculation) system where vacuum plays a major part. If you have a vacuum leak in the system or a faulty 'valve/solenoid' sensor part then your operation of the car (..and the idle) will be affected.

That is what you will now have to do...find the problem(s) area.

A) It could be a bad gasket(s) or cracked hose(s) for the vacuum leak(s) and/or....

B) faulty/bad sensor/solenoid or IAC valve

Here is my first suggestion: Try cleaning your IAC valve...the 'plunger' half.(See above 'How-To' link.)

BTW- Test for vacuum leaks. The leaks will be after the air filter box connection to the MAF sensor unit then along the 'elbow' bellow then to the TB (Throttle Body) unit then to the IM (Intake Manifold) then to the motor. There are more smaller vacuum hoses that are attached to the IM and sensors/solenoids.

Good luck!

Good clarification. djdevon3;That's the link I was thinking about , good catch.

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