idle problems
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Freshman User
Joined: Jun 2002
Posts: 41
Likes: 0
idle problems
I'm very frustrated with my 89 302. it won't idle right. it seams to stay around 1500rpms. i cleaned my throttle body and replaced the TPS sensor. sometimes when i stop it reves up to about 1700rpms and drops rapidly to about 800 rpms then reves up and drops again. it does this pretty quick as soon as it hits about 1700rpms it drops. I can't figure this out could someone please help me.
Thread Starter
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Freshman User
Joined: Jun 2002
Posts: 41
Likes: 0
idle problems
well i think i fixed it, but i don't know for sure. i unpluged the IAC? (the valve that bolts on the side of the throttle body). as soon as i unpluged it it idled like it should. its just hard to crank when its cold. does this mean that that sensor is bad?
Senior User
Joined: Jan 2002
Posts: 185
Likes: 0
From: Central Florida, USA
idle problems
My '92 had a leak in the air plenum manifold gasket. I found it by spraying carb cleaner around the joint between the manifold and the heads. As soon as it smoothed out I knew where the problem was. I had to replace the throttle body as well due to wear on the throttle plate assembly. More air was leaking than could be accommodated by the IAC, even after the gasket leak was fixed. I had 132,000 at the time and now with 161,000 all is still well.
Hotshot
Joined: Aug 2002
Posts: 12,679
Likes: 15
From: BC, Canada
idle problems
Sounds like the upper intake plenum gasket is shot and causing a vacuum leak. To replace it you have to remove the plenum which is a bit of a pain but not that bad.
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Senior User
Joined: Nov 2002
Posts: 158
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From: Champlin USA
idle problems
[updated:LAST EDITED ON 09-Nov-02 AT 09:53 PM (EST)]its a crap shoot!!! ive priced those damn idle control selonoids out, $70 at the auto parts store and over $100 through a Ford dealer. i was having bad problems with my idle too, much to my amazement i found there was no gasket between the throttle body and the upper intake!!! (i have no idea why) i'd say check for leaks or anything else around the intake that could be leaking. if everything looks good then go buy yourself a new idle control selonoid.
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Senior User
Joined: Nov 2002
Posts: 158
Likes: 0
From: Champlin USA
idle problems
[updated:LAST EDITED ON 10-Nov-02 AT 07:23 PM (EST)]i tried that on mine a while back and your right it was hard to start and keep running when cold (unthinkable for our winters here in MN). i suppose if you can live with the hard starts it prob will be ok. as long as it doesnt shut the engine down it will prob just throw a code and thats it. but then again who knows how they programed the computer to act.
Elder User
Joined: May 2001
Posts: 692
Likes: 1
From: Coon Rapids, MN
idle problems
You most likely have a vacuum leak that is letting unmetered air in at idle. The reason why it is hard to start when its cold is because since you have a vacuum leak (you can tell since it runs with the IAC off) only so much air can get into the engine at idle. When cold the engine will need alot more air to keep the idle up than it will when warm.
