Hi, I did several searches and still didnt get a definitive answer.
First off, I just finish replacing my IAT, CTS, Knock and TPS. In the process, I pulled out the IAC from the throttle body to clean and lubricate it. I noticed that the spring and pintle did not rock, retract or even move even with some force. When it was all back together, I started the engine and it idled smooth and correctly, however after 5mins or so, now it stumbles and stalls.(thats just sitting in Park) I am going to going to replace the IAC, Is there any sort of procedure to installing a new one, other than remove and replace?
THX

 

Remove the IAC again, then reconnected the electrical connector, put the whole assembly in a plastic bag, jumper the ALDL, and turn on the ignition. After about ten seconds, turn off the ignition and check the plastic bag. The pintle and spring should be out of the IAC and lying loose in the bag.

 

Thanks for the reply Vader, does that prove the old IAC is working or shot?
With regards to the new one, is that going to be just plug and play?
Because I had a few minutes, and my new IAC doesnt arrive until tomorrow, I removed the IAC again and finally depressed it to retract as much as possible. I did the IAC reset procedure but after I detached the connection and removed the ALDL jumper i went to start the car and I couldn't get the car to idle, it just died. I reconnected the plug to the IAC and it was hesitantly idling at 600 in park and 500 in drive. Does that sound like I definitely need a new IAC?
THX

 

That will prove if the IAC and ECM drivers are working. I misunderstood, and thought the new IAC was already installed.


As long as the pintle of the new IAC is reatracted fully before you install it, it shuold be a "plug and play" installation on a TPI.


That means the IAC pintle WAS fully closed, and all idle air was going past the throttle blades. Apparently, there wasn't enough idle air, or the engine would have run at 500 RPM like before. that means the throttle body needs to be cleaned, and the minimum air position needs to be reset - In that order.


No. It sounds like the IAC is sluggish. The fact that the IAC opened when you reconnected the electrical connector and allowed the engine to idle means the ECM driver circuit is fine, and the IAC is TRYING to move the pintle, and is doing it somewhat, otherwise there would be no idle (just like when you fully seated the IAC by jumpering the ALDL).

That should give you enough time to properly clean the IAC and throttle body bores and plates, lubricate the IAC, and reset the minimum air position of the throtles.

Idle Air Control Cleaning

You can remove the IAC and service it. Remove the electrical connector from the IAC. Unscrew the IAC unit from the throttle body.

You can gently rock the pintle back and forth and allow the spring to extend it until it comes apart in your hands. Clean everything with lint-free cloths and a mild solvent. Harsh solvents can affect the insulation of the stepper motor coils. It's generally the dirt and buildup on this worm shaft that causes sluggish IAC operation.

With the parts disassembled, measure the free length of the pintle spring. It should be around 2¼" long (MAF TPI setup - I'm not sure on S/D TPIs). If it has lost tension, you can carefully pull the spring to stretch it back to about 2¼" long.

When the worm gear on the pintle shaft is clean and dry, apply one ot two drops (no more) of clean light oil to the shaft and work the pintle back into the rack gears of the motor by the same rocking motion. It takes a while to get the pintle back into the worm gears, but you'll get it. It is important to get the pintle fully retracted into the housing so that the pintle is not forced against the gears when reinstalling the IAC unit in the throttle body.

When everything is clean and dry, replace the gasket if it is damaged, apply a little anti-seize to the threads, and torque the IAC to the proper specs. (13 ft/lb for '85-'89 , 30 in/lb for 1990-on.) Proceed with setting the TPS and minimum air position.

It takes only a little varnish and contamination to render an IAC almost useless. A little cleaning and lube will often restore it:



When it's all assembled again, repeat the procedure of jumpering the ALDL to extend the IAC, then disconnect the electrical connector from the IAC, and set the throttle stop screw for minimum air position. Use ONLY a handheld tach instead of the dash mounted tach for this adjustment.

Shut off the engine, reconnect the IAC connector, and wait at least 20 seconds before starting the engine to force the ECM to learn the new TPS position (if you moved the throttle blades).

 

That cleared things up a lot, thanks Vader. I did everything you mention and the car now idles without stalling. I also adjusted my TPS from .90 down to .77 As from what I searched on the boards about SD cars, that should be in line with spec. So I took the car out for a test drive and this is the results...From idle when you try to get the car moving, there is a lot of hesitation. During driving and you want to accelerate light or hard it is fine. Only from a stopped idle does it want to hesitate until I get a little speed up. That symptom is not as bad if I really go easy on the take off. From all the work I did, I cant see what this would happen from.

 

If you adjust the minimum air position of the throttles to maintain a 500-550 RPM idle (in DRIVE) with no IAC air, you can minimize throttle tip-in hesitation. You might also want to check the PCV valve to make sure it is the correct part for the engine. Correct PCV flow is important. While at it, see what the idle vacuum is.

 

OK...here's an update. I again re-did the minimum air adjustment, twice this time, one prior to and once more after a test drive. A second time was needed because it didnt fully work. Well on that second time there was minimal to adjust, however I did do soemthing that I did not do in my prior attempts...when it was all ready to go I turned the ignition on/engine off and let it sit for a while. Since then my car has been running normally (knock on wood). I also change the PCV after that just to finish it off. I'm not sure how important it was that I did the ignition on/engine off thing, but it is now running fine. Thanks for all you help Vader.

 

What are you jumpering in the ALDL? top right 2 pins? A&B?