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Unread 10-08-2009, 04:19 PM   #1
bjl95mustang
Registered User
1998 ZJ 
 
Join Date: Dec 2005
Location: Austin, Texas
Posts: 805
Intermittent rough idle cold and hot.

In the mornings I will stop for gas about 1 mile from my house. When Iím pulling out of the lot it will stumble when I accelerate. But on the highway itís fine.

After I have been driving for a while and she is nice and warmed up I have some issues. When Iím sitting at a light my rpmís will drop and I can my engine stumble. It seems like itís miss firing. But once Iím moving she is just fine.

I just did a tune-up a couple months ago. Cap, rotor, plugs, and the wires are about 2 years old.

Where should I start checking? I have not had a CEL.

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Unread 10-08-2009, 04:46 PM   #2
melk
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1996 ZJ 
 
Join Date: Sep 2009
Location: Charlotte, NC
Posts: 2,891
Have you cleaned the IAC? Checked out the TPS?
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Unread 10-08-2009, 05:34 PM   #3
cmonson
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Join Date: Nov 2006
Location: Columbus
Posts: 1,546
when this starts happening, and you don't have any codes, I would start by taking your throttle body off and cleaning it so it looks like new. This could help, and the costs are free.

If that doesn't do the trick, then I would replace the IAC, then the TPS.

On a 98 (12 years old) the TB could be very carbonated and thus create problems. Clean out the small orface very well also.
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Unread 10-08-2009, 05:55 PM   #4
gomes512
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1994 ZJ 
 
Join Date: Nov 2005
Location: Des Plaines, IL
Posts: 1,143
stumble upon acceleration usually indicates a tps that's on the way out. You can further diagnose by idling in park and very very slowly depressing the accelerator a little by little. Usually a bad tps will not notice this slow change until you've depressed the pedal a good bit. Then it will jump up to say 1K or so, so you should see a hesitation. When this jump occurs keep your foot at that position and release the pedal very slowly to the end, it will most likely cause a rough idle.

If changing the tps I would just get a new iac to go with it, two birds one stone.
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