djdevon3

Checking The Idle Speed & Idle Air Control Valve

12 posts in this topic

This question comes up almost on a daily basis so it's best to make it a sticky as it will certainly be referred to in the future.

This is straight from the 1997 Workshop Manual so it's likely to be a different procedure for 93-95 due to being an OBDII manual.

Idle Speed Adjustment (FS MTX)

1. Turn off all power consuming accessories.

2. Verify the idle speed is within 650-750 rpm. You want to be at 700 rpm ideally.

3. If not within specification adjust idle speed.

4 Connect data link connector terminals TEN & GND by using a jumper wire.

img-315842-1-OBD1_Diagnostics_Pinout.gif

Caution: Throttle adjusting screw is set at the factory and must NOT be adjusted. Any adjustment will negatively effect engine performance.

5. Adjust idle speed by turning the air adjusting screw until smooth running anywhere between 500-800 rpm.

img-315842-2-Idle_Speed_Adjustment_FS.jpg

6. With A/C on you should expect to see rpm anywhere in 725-825 range.

7. Disconnect the jumper wire.

Idle Speed Adjustment (FS ATX)

1. Turn off all power consuming accessories.

2. Using the SST (NGS), verify that the idle speed is within the specification.

3. Verify the idle speed is within 650-750 rpm. You want to be at 700 rpm ideally.

4. If not within specification, race the engine and operate the A/C with no load.

5. Stop racing the engine and the A/C. Check idle speed.

NOTE: Using by NGS tester and must be cleared any DTC and pending trouble code when you reconnect the IAC valve connector.

6. If idle speed below spec

- Disconnect IAC valve connector and check the engine speed.

- If the engine speed does not change, inspect IAC solenoid valve.

- If engine speed changes execessively or stalls, inspect the PCM and IAC solenoid valve related wiring harness and connectors.

7. If idle speed above spec

- Disconnect IAC valve connector and check the engine speed.

- If engine speed does not change, adjust with the air adjusting screw (AAS) until smooth running anywhere between 500-800 rpm.

img-315842-3-Idle_Speed_Adjustment_FS.jpg

- If engine speed changes execessively or stalls, inspect the PCM related wiring harness and connectors.

8. With A/C on you should expect to see rpm anywhere in 725-825 range.

Idle Speed Adjustment (KL)

1. Turn off all power consuming accessories.

2. Verify the idle speed is within 600-700 rpm. You want to be at 650 rpm ideally.

3. If not within specification adjust idle speed.

4 Connect data link connector terminals TEN & GND by using a jumper wire.

img-315842-4-OBD1_Diagnostics_Pinout.gif

Caution: Throttle adjusting screw is set at the factory and must NOT be adjusted. Any adjustment will negatively effect engine performance.

5. Adjust idle speed by turning the air adjusting screw until smooth running anywhere between 500-800 rpm.

img-315842-5-Idle_Speed_Adjustment_KL.jpg

6. With A/C on you should expect to see rpm anywhere in 775-875 range.

7. Disconnect the jumper wire.

Idle Air Control Valve (FS MTX)

1. Start engine and run at idle

2. Disconnect IAC valve connector and verify that the engine RPM changes.

3. If the engine condition will not change, do as follows:

-a- Connect the SST to the data link connector-2.

-b- Verify diagnostic code P0505 is not displayed. IF shown carry out troubleshooting for code first.

-c- Change duty value of the IAC valve to 100% by using the simulation function and "Idling Test" and verify idle speed increases.

-c1- If speed increases: replace ECM.

-c2- If no speed change: replace BAC valve.

4. Warm-up engine to normal temp and run idle.

5. Turn electrical load ON and verify engine speed is within spec.

6. With A/C on you should expect to see rpm anywhere in 725-825 range (exclude temporary drop during accessory toggle)

7. If not as specified check related switches and wiring harnesses.

Idle Air Control Valve (FS ATX)

1. Start engine.

2. Disconnect the IAC valve connector and verify engine speed changes.

3. If engine speed does not change do as follows:

-a- Check IAC valve

-b- Perform IAC valve PCM terminal voltage test

-c- Check IAC valve air passage

4. Warm up the engine to normal operating temp and run at idle.

5. Turn electrical loads ON and verify engine speed is within specification.

6. With A/C on you should expect to see rpm anywhere in 725-825 range (exclude temporary drop during accessory toggle)

7. If not as specified check related switches and wiring harnesses.

IAC Inspection (All Engines):

1. Disconnect IAC connector.

2. Measure resistance of the valve.

Resistance should be: 7.7-9.3 ohm at 73F

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There is definitely a problem with mine, then. It idles around 900, and drops sometimes to around 600 when the a/c is in use.

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There are many things that can affect idle. This article only covers adjusting the idle air screw. Recommend creating a topic in the appropriate technical support forum so you can get help on your issue. It might not necessarily be related with this article.

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does anyone know the factory setting for the screw (e.g close it and CCW 2 revs or smth..).. since i have no TEN pin where it should be and no GND where it should be, i just messed with the screw temporarily...

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There is no official information pertaining to the default setting of the AAS. Techs aren't even supposed to mess with it but of course during the life of the car sometimes they do get messed with. In order to attempt at resetting the screw to a desired level thread it all the way and back out by 1 1/4 turn. It might require some fine tuning in conjunction with your throttle stop screw, distributor (4th gen). Make sure you have base timing mode open for programming (4th gen shorting pins or 4th gen ATX requires shorting bar). All of this requires that your mechanical timing (crankshaft, camshaft, and timing belt) are set correctly (perfectly). It is preferred to have this type of service performed by a professional. If you want to attempt it at home by yourself and you screw it up please take it to a mechanic for service. It requires fine tuning adjustments which no one on this forum will be able to walk you through due to the variable settings each components might require. It's like flipping knobs and turning dials at the same time to accomplish a good tune on your radio. It takes experience and best left up to a professional for the best results.

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yeah.. i'm well aware that it's something you should leave alone. :D

but a real pro gave me this advice to raise the amount of idle air and he said his car is running well for almost 3 years now.. I guess i should look for another throttle body of course, but tomorrow i'll try to measure the fumes again.

all the fuss is about extra air in the exhaust at idle.. nothing wrong when rpms are raised.. i checked the piping, not a single leak there, so i guess the problem lies somewhere within.. thank you tho. I'll make a vid later and post it in my thread.

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Here's the bad thing about that. If your car is running incorrectly then adjusting the AAS is only a temporary measure. If whatever is causing it gets more out of spec then eventually you'll have no more adjustments (turns) to go and be forced to deal with the issue... by then the car is likely running overly rich or lean causing incorrect A/F ratio (bad MPG). I'm not an advocate of band aids unless needed. If you are in a position to get it fixed right the first time then do it. That's why AAS adjustments are frowned upon. It's just ignoring the real issue.

With that said sometimes owners here need that info to fix an incorrect adjustment done by a previous owner after they get the car fixed correctly. It's another fine tuning knob that just makes things more complicated in the future for yourself, a future owner of your vehicle, or a mechanic (costing more time/money). AAS adjustments are not something that anyone on this forum should ever advocate. With that said if you plan on making a video on it I'll definitely watch it because I love anything to do with 626's anyway. Please remember not to advocate it as a fix and let the viewer know that it's not a good thing to do unless absolutely necessary.

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Don't worry, friend, i won't blame you. I did finish the tech school, so my degree says i'm a mechanic... i take it as a challenge. yes, you are correct it's only a temporary fix, but i need it only for the next two weeks and i'm facing another MOT test. So i need it only that much..

I failed to make a video, since my girlfriend made a sh*tload of pictures of our cat...

Today i woke up with some more enthusiasm about it, took my car for a drive, gave it a good spin and then took out my flathead screwdriver and let the party begin. At first, i must punch myself - in september, when i replaced TB's gasket, i guess my head was high and i forgot to tighten the clamps of the air duct... Embarassing huh?

That done, i closed the air screw and managed to find a range, where the engine was not bucking anymore. Even the muffler didn't spit that much.. Nice and steady idle @ 750-800 maybe.. Some things got better - when driving and putting it in neutral, the revs would drop from 2700 to 1500, then hesitate a bit and then POW 400-500 and then back at idle.. This was last summer, after i found a leaking TB gasket.

But the problem never went away. I recently bought new spark wires.. Tho the cheapest ones, they're still better than old ones.. So the problem decreased even more..

But i've developed a hissing sound now. Coming from under the intake, so i guess it's the resonator, that's leaking, After i turn the key off, i hear a long "hisssssss..." the hissing goes away after 1000 rpms.

It's still -25*C here outside, so i'm not getting myself frozen yet, but when it gets milder, my plan is to take out the intake and clean it thoroughly.. Also i found that the injector on cyl. no.2 is ticking not as loud as the other 3.. so my best guess i might have a weak injector too...

Today i drove about 150mi and so far better than ever. It doesn't even sledgehammer me, whenever i press the accelerator when driving.

Damn, i guess i really should make a video, in english and some comments, just for you guys. :)

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That would be awesome. If you have the ability to make a video I'd enjoy seeing your progress and what you're doing. Could help a lot of people. I think the hiss after shut down is normal for a 626. My ATX and ND28's MTX does it. I think it is from releasing the vacuum pressure in the manifold.

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Found this link which give the procedure, but it seems to require a scan tool:

 

ALLDATA Online - 1998 Mazda 626 LX L4-2.0L DOHC - Adjustments

 

It's a really weird procedure.

Also found this:
 

Re: 1998 Mazda 626 idles rough. How can I adjust idle speed?

 

I have a 1993 and the same problem. To adjust the idle the computer needs to be re-adjusted. Place a wire between TEN en GND inside the diagnoses connector. Adjust the idle with the flathead screw on the right top side of the t throtthle body. Rotating counterclockwise will rise the RMP. Turn the car of and remove the wire. I have tried it and the RPM are now 950 rmp but it is still a little bit rough. Also cleaned the EGR valve, clean the IAC valve, cleaned the injector etc....

 

 

 

I remember that I had to do something similar on my 97 323...

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