Rough Idle After Engine is HOT

jranin · 05-09-2008, 08:58 AM

Our 98 Windstar starts to idle roughly after the engine has gotten hot from rough driving (stop and go) or a certain period of time being driven unles the gear is in Neutral. I was told that it could be either the EGR Valve or IAC solenoid, so I changed them but the rough idling under these conditions still has not gone away.

What else could cause this?

Thanks.

vindctar · 05-09-2008, 09:58 AM

Go here for troubleshooting rough idle when engine is hot: http://www.autozone.com/servlet/UiBroker

adrenochrome · 05-11-2008, 02:19 PM

Do you have a "check engine" light on?

mpeoples · 05-13-2008, 07:15 PM

If you are experiencing this after the car has been sitting 10 - 20 minutes (some period less than an hour, but more that a few minutes), then the problem is fuel leaking through the injectors. I have a 1989 Aerostar and a 1996 Windstar. Both exhibit this problem. A friend of mine who is an auto mechanic says the problem is inside the injector, and there's not much you can do about it.

If the problem goes away quickly, particularly if you rev the engine, then my guess is that this may be the problem.

The fuel injectors may also be involved in a different way. My 1996 Windstar was idling very rough after it warmed up. This problem did not go away like the problem described above. The solution was to replace one of the fuel injectors. I had a check engine light and DTC P0303 (Cylinder 3 misfire). I moved the injector to the #6 cylinder, and sure enough, the problem followed it. $ 60 to NAPA later, the problem appears to be solved.

What's happening is that as temperature rises, the resistance in the coils that drive the injector goes up. As the injector degrades over time, the ignition system can't overcome the resistance, to injector begins to fail. It works when the engine is cold because resistance is lower.

Hope that helps.

jranin · 05-25-2008, 12:35 PM

Thanks, mpeoples. When the rough idling happens, what I do is turn and leave the engine off for a couple of minutes and the issue goes away, at least until it gets to a certain temp. But, I'll have the injectors checked.

phantom_smack · 05-25-2008, 12:50 PM

Do you have any codes? I have seen a rough idle when warm from leaking intake o-ring gaskets and isolater bolts.When you are in there replacing them make sure you clean the egr ports.This all can be done without removing the cowl so its not as bad as it looks.

BroncoJoe19 · 05-31-2008, 04:50 AM

Pull codes again. Assuming that the IAC is good because you just replaced it, check your wiring to it, to make sure it is getting the proper voltage. Poor grounds *could* cause your problem.