Rough running when cold..

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Sep 29, 2004 | 05:39 PM

mspence

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Joined: Sep 2004

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From: Avon, IN

Rough running when cold..

I have an 89 with the 302 and about 100k miles. When I start it up cold the engine revs to about 2k rpm for a few seconds and then comes back down slow, then dies. If i give it a little gas and rev it up for 30 sec or so it idles fine. I have new rotor, plugs, wires recently. Any suggestions?

Sep 29, 2004 | 11:48 PM

greystreak92

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Joined: Sep 2002

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From: Gateway to the West

Sounds like a dirty IAC. Under normal conditions, the PCM will rev the engine higher at startup for about 20-30 seconds if you just start it and don't tap the pedal or put it in gear. After that time, the rpms will be brought back down by the PCM. This is all controlled by the PCM via the IAC solenoid/valve and several other sensors. Sounds like at normal idle the bypass passage is a little too tight to support the air requirements of the engine prior to being fully warmed. Try cleaning the IAC valve first and see what kind of results you get. You will have to remove it to clean it well. A new gasket between the IAC and the throttle body would be a good idea since you will be separating the two components. Do the rest of the throttle body while you are there...couldn't hurt.

If this doesn't help, check to make sure the IAC solenoid is actually functioning.

Last edited by greystreak92; Sep 29, 2004 at 11:51 PM.

Sep 30, 2004 | 08:52 AM

coolcat3406

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There is also an ACT Air Charge Temperature sensor located on the drivers side of your lower intake manifold. This tells the PCM what temperature the air is entering the engine. They are usually pretty cheap.