Idle problem

[Rommel]

Having a problem with the idle on my 84. Once the water temp gets above about 140 the problem begins. The car will idle normally for about 5 seconds after coming off throttle but then drops to about 500 RPM. It stays here for about 10 seconds and then returns to normal. This cycle continues and has sometimes stalled compleatly. I had the codes scanned and it came up with #26: Mass Air Flow Meter out of range. I replaced it with new but the problem persists. Other notes. The oxygen sensor only has about 5K on it, I can find no vacuum leaks and the engine is in stock form except for a K&N. The EGR valve is also operating normally and both fuel pumps are relitevly new, less than 30K on them.
I rely on this car for 90% of my driving, Please help!
R/Brian.

[richsvo]

Rommel,
(not saying this definitely the cause) but mine will do this from time to time, and the cause is always the IAC. I broke off the tab that holds the plug for it together, and sometimes it works its way loose. Once it was because the IAC was a little clogged up, so a good cleaning could be in order. Like I said, not saying this is what it is, but might be a good place to start...
HTH,
Rich

[Rommel]

Thanks for the reply Rich,
I thought of the IAC also but am trying to avoid throwing $ at the problem until I am sure. I'm still hurting from the $90 I spent on the AVM. I will take a look at the IAC connection today. I recently cleaned the TB and the IAC ports were clean.
Thanks,
R/Brian

[GAboySVO]

If it is only happening after a certain temperature then it might be related to the ECT. When you checked the codes, was the car cold or hot? Some times the ECT won't give an error code because the voltage is based on engine temp. You might want to check the voltage at cold then at the temp the problem start to see if it matches to what is expected.

[Rommel]

The engine was at operational temp when the scan was conducted, otherwise I got a coolant temp out of range. Still I only got #26 AVM out of range. I have not done a scan since I replaced the AVM so I will do that again to see if it was covering another code.
Thanks for the info.
R/Brian

[richsvo]

Rommel,
Sorry...I wasn't implying that you should replace it, just make sure it is clean, and you have a good connection.
Rich

[Rommel]

Thanks Rich, That's exactly what I will do.
R/Brian.

[Gator]

while your fiddlin' round there, might wanna just take off the IAC and give her a douche with some brake cleaner. Carbon build-up in there gets pretty nasty.

And reset the TPS when yer all finished

[Rommel]

Found a post in the Lounge section concerning TPS and IAC adjustment procedure. Think I will try that this weekend. Any other suggestions are welcome.
Thanks,
R/Brian.

[KevinK]

Another overlooked item, exhaust leaks. My idle was hunting sometimes and other times it was fine. The new exhaust system cleared it up.

[Rommel]

Found the problem! The IAC was carboned up. I had it off in the beginning but didn't see the problem. I took it off this weekend and shot it with some brake cleaner. Got all kinds of black crud out of it.
Thank you to all who contributed to my troubleshooting efforts. The car runs great again.
R/Brian