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Stanthe626man

Rough Idle Issue

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Hello all,

 

So I have read these forums for about 1.5 years trying to figure out what is causing the rough idle on my 99 626 V6 auto, so i decided to create my own thread on the issue.  When the car is in drive, and warmed up, the car idles very roughly at a stoplight. I have found that it doesn't appear to idle as rough when the engine is still cold. In neutral the car doesn't vibrate. Specifically the car idles very roughly and the occassional dip in RPMs occurs. At idle in neutral, the gauge reads 740-750rpms, while in drive it reads about 690-700. Most of the time it's just a very rough idle without a huge noticible misfire and not too much RPM fluctuation, but when it's in drive and the RPMs do dip, its usually a powerful rumble you can feel in the engine with a fluctionation from about 650-700. The dip in RPMs is intermittent. It usually starts after about 3 minutes of driving and i come to my first or second stoplight, then it occurs many times throughout my trip after that.

 

To add to that issue, here is something else i recently noticed as a symptom. When I turn on my inside air when i'm sitting at a stoplight, the car vibrates real bad for about 2 seconds then returns to a somewhat normal RPM level, about a hair under what it was before i turned the fan nob on. You REALLY notice it when you quick turn the nob from 0 setting to 4, but you can still feel it cause the entire engine to rumble greatly when you turn that nob from 0 to 1, 2, 3 or whatever. With that said, does that imply a grounding issue? Grounding and/or coil pack issues? Something else? I tried turning my lights on real fast and head unit, but those didn't seam to cause the engine rumble like the fan did (maybe they are just not noticeble enough to the driver?)

 

Next issue, possibly related. I recently had some work performed by a friend mechanic, and i also did some tune up procedures over the last 1.5 years that i have detailed below to help with the idle. My friend had replaced the valve cover gaskets on both valve covers because the car leaked oil from both covers ever since i bought the car 9 years ago. So that fixed the leaks, not a drop under the car for about 4-5 months, then slowly a drop, then multiple as time went on. Now, about 11 months after the front gasket was replaced, the gasket has splits on the left and right of the front valve cover, i don't think the rear has any leaks (yet). I don't know if this implies bad mechanic installation or pcv issue, but keep reading on about what i have also done!

 

So here is what has been performed on the car since i started with all this.

-Checked for vacuum leaks with starter fluid, multiple times. Found nothing.

-Replaced PCV valve and gromet with oem mazda (i tested the new pcv valve before installation, it worked good.

-Cleaned PCV hose to intake manifold, and there was no residue of any kind built up. Was pretty clean really. I also cleaned the port the hose attaches to at the intake manifold, also not too bad.

-Cleaned throttle body (did not remove IAC from TB) after i removed from the manifold, and I also cleaned the EGR ports right inside the intake manifold.

-Replaced throttle body gasket when reinstalled TB

-Replaced air filter (mazda oem, i used an 01 filter since that's what the dealership ended up giving me, i assume it's the same filter for my 99)

-Replaced fuel filter

-Cleaned MAF wire (sensor was replaced about 8 years ago, but seems to function fine from what i can tell)

-Replaced Spark plugs and wires with NGK recommended ones.

-New Battery about a month ago (old one went bad anyways, lasted 4 years).

-I have used techron concentrate 3 times in the last year, and i have used fuel injector cleaner (lucas) for many tanks as well.

 

What my mechanic friend did

-Replaced water pump (didn't have to remove timing belt)

-Replaced valve cover gaskets

-Replaced intake manifold gasket

-Replaced the passenger side motor mount, driver side transmission mount, and the "dampener" underneath that bolts to the crossmember with beck/arnley mounts (seemed well made for aftermarket). However, we could NOT find factory OEM mounts for the front and rear, or even beck/arnley mounts, which is what we used for the 3 we replaced. I found 2 DEA months that were the right design, but the througbolt hole ont hose DEA mounts DID NOT MATCH the bolt that comes with the car, so i refused to put them on and put the old ones back in. I would not allow rattling aftermarket mounts to be installed. By the way i watched as he did all these repairs at his shop. The rear mount is in very bad shape, and the front is very worn as well. I know this is not helping the vibration issue, but the motor isn't running right at idle. So i can replace the mounts, but i feel all i'll be doing is masking the issue, that's if i could ever find the dang things. (anyone know where i can still get OEM mounts for my exact car, 99 626 V6 Auto? because 5 dealerships i've called all say i'm SOL in finding one from a mazda dealer)

 

This rough idle started and was about as bad as it is today before I attempted everything i listed above and well before my friend mechanic performed his work. I am at a loss on what next to do. I have not tried the following,

 

-Have not tested fuel pressure (because i didn't think this mattered if it accelerates and operates well under high throttle, am i wrong?)

-Have not pulled the 6 injectors out to inspect for dirtiness (because i didn't think this mattered if it accelerates and operates well under high throttle, am i wrong?)

 

So with all that said, should i give up, or do any of you have advice as to what next i should do or even redo or test further? I hope i have including everything that will help the experts figure out my neverending rough idle. Thanks in advance just for taking the time to read my issue!

 

-Stan

 

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Quick update!

 

I just decided to test my theory on bad grounding. Here's what i found.

 

With negative ground cable disconnected, my MM read 12.73volts. with the negative MM prong still attached to the negative terminal on the battery, and the positive prong attached to the car's negative ground cable, it read 11.2 volts. Did i finally found my problem? and if so, do i only need to route a new negative cable to the frame of the car?

 

Or is this just one of many potential issues?

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Hmm. I was going to guess spark plug wires, until I read you had replaced them.

 

Do you get the same symptoms when you turn on the rear defrost, or press the brake pedal, as when you turn on the fan?

 

That 11.2 volts does sound too low. There is a main ground wire that attaches to the top of the tranny. That is a common source of problems. I suggest you clean up that connection, before replacing the negative cable.

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Ok finally an update, had a lot to deal with lately.

 

To answer your questions NickR, yes all those things cause the car to run rougher when turned on. The car runs best when all electronics are off. I cleaned up the ground wire and the connection where it is crimped to the car's frame. Once i did that the same problem still existed (although maybe a little better than before), so i decided to replace the ground wire with a 2 gauge wire, and I also applied a ring terminal to the wiring that goes to the coil pack, etc. It didn't appear to help much, definitely didn't hurt. Then, i pulled off the main connecter to the alternator (which was replaced about a year ago), cleaned it with electronic cleaner and put it back on with no change in symptoms. Where's the ground connection for the alternator? Any other suggestions?

 

MADMATA, so just replacing the ignition coil solved the rough idle with electronics/accessories on? I thought about replacing this since it's one of the last things i haven't touched, mainly because i figured if it was the accessories being on causing this, it kind of implies that the battery/alternator couldn't keep up with the required juice, and since i've replaced both in the last year, i'm leaning towards wiring. Can you or someone explain the logic on how replacing the ignition coil would solve this, without touching any wiring? Since it's a somewhat pricey part to replace I would like to know more before replacing.

 

Thanks!

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An old ignition coil is similar to having an old and degrading magneto for your lawn mower.  If the internals start degrading then you'll have higher resistance internally.  That means a weaker spark.  Weak spark means misfires which will always = rough idle.  You should test the resistance of your coil and compare that to factory specs which can be had at pmx626.info (look it up in the work shop manual).  Don't just go replacing parts because what fixes something for one person might not fix it for you.  That's like going to the doctor to complain of a stomach ache.  One person might have indigestion and the another person might have ulcers.  It's not always one size fits all which is why we preach diagnostics here.  If you go and replace the ignition coil without testing it first and then come back to say it didn't work then I'm not going to respond or help you. 

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i guess i just need to take it to a shop for a computer to verify what is wrong. The same issue is with my 2001 ford escort. i hear they are the same in a lot of ways. im not going spend the time to take my coil to some place to test my coil. It would be cheaper and more time appropriate to just change it out by guessing. if i had all the tools to verify all my problems then i wouldn't need a website to ask and have a response of "im not going to respond or help you" ... wow you must be single and a lot of time on your hands. Thanks anyway.

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If it's not the coil then replace the MAF sensor next, then IAC, then O2 sensors, then plugs/wires, then coolant temp sensor, then valve cover gaskets, then injector O-rings, then the 20 other things that can cause a rough idle.  After you've spent $1000 from guessing and changing parts then maybe you'll understand the importance of diagnostics.  If you want to learn your lesson the hard way I'm not going to stop you.

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i just like to find out where i can buy all thoes sensors for $1,000? Cheap if you know that just alone of the idle sensor is $301.99.

guessing and changing parts is what i can do. unless you have time and or a computer. i hope you understand i am trying to keep 7 cars on the road

i have a 2000 honda odyssey (love it),  2001 buick lesabre, 2000 buick leasbre, 2001 ford escort, 1998 chevy astro, 72 mg midget, and now a 2001 mazda 626

my thought is always that if it is easy to change out....do it....it might be a part that needs to be changed out later....the more new parts you put in a car, the less suprises you will have later on.

when i buy a car, the first thing i do is change the belt, change hoses (the easy stuff) so i dont get a phone call later while someone is on the road. the mazda runs but not perfect, along with the escort, so again i need to say that i will take to a garage for them to put it on a computer to figure out the idle problem, then do the same to the escort. They both have the same idle issue. 2 for one pricing

hopefully less than $1,000 for repair cost. im not going to tackle this issue with the forcast of -5 deg in a unheated garage tonight. so i am willing to pay up rather than play the diagnostics ( educated guessing) . i hope you understand the difference of guessing and educated guessing.....time.....new parts are never a bad investment. it is always cheaper than taking it to a shop.  im glad you will not stop me from learning. but i do need to know if i diagnose the "whatever" part and then change it....that one part will do it...............probably not....there is usually more than one issue (part) needs to be replaced or cleaned when you purchse a used car.

i truly think you don't understand that we are both guessing. your guessing is more in detail.

Off to the shop. Later.

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Yes to change out is usually easy. But changing out all these parts with what you would call cheap parts is not a good thing. Sure you can go the auto parts store and get belts and hoses. If you start changing out all your sensors with these after market parts you may end up with some sensor somewhere not working correctly. Then you will really be in bind because you will dismiss this part as bad just because it is new. Just because the part is new does not mean its better ( unless you are buying directly from Mazda ). 

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New is not better, you're kidding yourself. Basic diagnostics take an hour or two, ask you need is a multimeter that costs about $8, and and obd ii scan tool, at around $40. These two tools will let you diagnose almost any problem with the electronic engine control system.

Also there is no such thing as an idle sensor. There is an idle air control valve (actuator), and an idle switch in the throttle position sensor (indicates to the ecu that the throttle is completely closed).

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  1. sorry my old school thinking is that working with chevys, replace the part anyway the replacement parts are usually better than the installed or factory.

and the idle sensor.....potatoe patitatoe.....same thing.

some new parts can be better, dont kid yourself. i used a ford part in the mazda...imagine that

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i guess i just need to take it to a shop for a computer to verify what is wrong. The same issue is with my 2001 ford escort. i hear they are the same in a lot of ways. im not going spend the time to take my coil to some place to test my coil. It would be cheaper and more time appropriate to just change it out by guessing. if i had all the tools to verify all my problems then i wouldn't need a website to ask and have a response of "im not going to respond or help you" ... wow you must be single and a lot of time on your hands. Thanks anyway.

 

If the ECU isn't flagging something as an error, you may end up empty handed. Try working on older cars for diagnostic ability. No magical printout to work by. DJ knows his stuff, you'd be wise to take it on board :thumbsup:

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i guess i dont understand "take it on board" ? oh well this site must be for mechanics and not for the common folk trying to get by and just make a car get from one place to another. i can make older cars run....but the new ones 2000 and newer are too much for the average Joe to learn new. I guess i just need to find a good mechanic and pay. sorry to bother everyone. Would anyone like to purchase a 2000 mazda 626 (built by Ford)? i am looking for a good toyota.

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I don't think a single person who had replied on this thread is a mechanic. In fact, only cheesy mechanics throw parts at a problem until it goes away. Reputable ones perform a diagnostic to isolate the problem. Getting mad that technology isn't stuck in 1980 isn't going to help you, nor is being dismissive when you don't know or understand something. This site is a learning resource, if you didn't come here to learn, why did you come here?

If you think a Toyota is going to work any differently you are mistaken. Newer cars get more and more complex, that's an unfortunate reality. Virtually every part your Mazda has will be present in some form on any reciprocating engine with fuel injection.

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Sorry just my opinion. I have never been able to find an aftermarket new part that is better in quality than my original mazda part (exception would be hoses, spark plugs, wires). When my coil went out. I went to auto zone and just by inspection I could see the poor quality compared the the mazda part. So I ended going to a wrecking yard and picked up a few for cheap. Still on the one replacement. 

Correct I am not a professional mechanic, but I get by. I don't think anyone here that replied said throw parts at it. We are all for proper diagnosis. 

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Even aftermarket PCV valves aren't as good as a Mazda PCV valve.  Cheap chinese parts vs quality japanese parts.

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If you are still having the rough idle issue you might have a air pocket trapped in your radiator hoses which is affecting your ECU coolant temperature sensor which does cause a rough / fluctuating idle. With the engine cold, start the car take off the radiator cap and put the garden hose in with the tap turned on full blast and fill the radiator with the engine running, keep going until the water overflows for about 30 seconds then leave the radiator cap off and let the engine warm up to running temp so the thermostat opens up with the radiator cap off, then get the garden hose again and put it in the radiator again and hold the rpm at about 1500 while filling, even if the water is overflowing already. Then with the revs steady at about 1500rpm put the radiator cap back on, when the cap is on let the accelerator off and the air pocket will be forced out the radiator overflow hose.

If that doesn't work replace the ECU coolant temperature sensor

It costs around $50

The sensor will cause a rough fluctuating idle if it's faulty or there is a air pocket in the cooling system.

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Don't just replace parts.  Test them.  You can test if your coolant temp sensor is faulty instead of paying money for a new one.  Don't be a parts changer.  Diagnose the issue.  Get a factory service manual from pmx626.info that has every testing procedure you could want for every component on your 626.

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Can you pull some realtime data with Torque app?

 

Like how many misfires in one drive cycle, the O2 readings when this happens etc... Even there is only 1 or 2, you will feel it during idle.

 

I have had a coil pack problem like this before. But that thing was actually causing intermittant misfire to be registered. (Not enough for check engine light.) As DJ and Snail said, you have to actually know the problem before replacing parts. (I did this before though I have OBD2 scanner, step by step, I learned as well with the help from DJ and Snail.)

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So, the coolant temperature sensor causes a rough idle? No wonder I keep having issues after a cold start with my '95 HGM ES. I wondered why it would drive fine at first, then drop back to a rough idle. Thanks for this solution, I changed all the plugs/wires, distributor cap/rotor,  cleaned the intake/TB/TPS, the fuel injection system, and Seafomed the old oil before the oil change, the idle was back to normal on a cold start. I let it warm up and BAM! Rough idle, and it struggles to pull hills. I didn't realise that a faulty temp sensor/air in coolant had such an effect on the idle. I know I may have to replace a few more things, it being a '95, but it just baffles me that this small issue affects the drivability of the car. If you're wondering, this is Old Six:

20180624_124350.jpg

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