Just had problems with idle on my 1991 with only 56k miles on.

Car would start normally with rpm at 1300 but after first gas pedal push it would fall to 500. Things came back to normal after it start to warm up.

I took out the IAC and cleaned it with carb cleaner and blew air to dry it. It does open with 12 volts and seem to move freely. Did not seem to improve anything not to say it works less well than before clean up.

I removed and cleaned the throttle body and checked that the throttle position switch is working as by the green book. That is fine and the continuity is good on the middle and one side connector. The other side does not seem to have continuity with any throttle opening.

I replaced the IAC with an old one I had on hand which seem to work as I just started the car.

The IAC I took out has a strange 1/16 inch gap at the swing valve when closed. In fact it is not closed as I can blow air through with my mouth. It seems the rest seat is worn and the gate moves past the closed position.

Question:
Can I re-adjust the sealed allen screw on the side of the IAC to move the gate properly closed ?

"Question:
Can I re-adjust the sealed allen screw on the side of the IAC to move the gate properly closed ?"

You could, but you shouldn't. It isn't the cause of your symptom, and it won't cure it either. The at-rest opening is the limp home airflow around the throttle, for when and if the ECU adopts limp-home map. It may get you across the railroad tracks one day. It is there for safety.

Much is not understood about how this valve works. Baseline setting (which adapts to the wear of the car like vacuum leaks and valve wear) is not when no voltage is applied to the valve, but when a low duty cycle control maintains the opening well past that rest point, on the other side of the valve's vane. The baseline must allow for flows above and below to properly regulate idle at varying engine temps and air requirements.

This gap is normal.



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Art Benstein near Baltimore

He often broke into song because he couldn't find the key.

I am happy to hear that this gap is normal and used for the limp-home.

I was asking because the other used IAC I put in does not have that gap which made me think the one that was on the car may be defective or worn.

Thanks a lot and I will be watching closely how it goes and keep some tools in the trunk just in case. I also read that a defective ECU could be the problem. My 561 ECU has the white Volvo sticker covering the pink Bosch label.

I always keep a spare ECU, an AMM and an ICU with the car.

"...other used IAC I put in does not have that gap...

Interesting. I will assume you found the Glyptal unmolested on that used IAC or you would have noted that in your response. Makes me wonder how many others want to tweak that adjustment.
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Art Benstein near Baltimore

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