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Old Jun 17, 2009 | 08:25 PM
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Default rough idle

My 98 c-5 has a rough idle at times. When the
engine warms up or after driving hard it gets worse.
Does anyone know what that is and how to fix it?
Help.
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Old Jun 17, 2009 | 08:38 PM
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My '98 has the same....I and some passengers actually like it...feels like an aggressive cam
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Old Jun 17, 2009 | 09:23 PM
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Default rough idle

LOL!!
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Old Jun 18, 2009 | 01:33 AM
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Try changing your plugs and wires to start. From there probably look into the coil packs / check fuel pressure.

Is it throwing an engine light?

If not probably just needs tune - up items - plugs , wires, fuel filter, air filter etc..
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Old Jun 18, 2009 | 07:11 AM
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If you want help you need to supply more information than what you have.
  1. How many miles on it?
  2. What mod's if any have been done?
  3. Is this a new issue or has it been this way for a while?
  4. What fuel are you running and have you used any fuel additives, if yes, what?
  5. What is the idle speed?
  6. You mentioned that it gets worse after warming up, what temp?
  7. Do you have any error codes?

Last edited by Eric D; Jun 18, 2009 at 08:20 AM.
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Old Jun 18, 2009 | 08:06 AM
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cound just be needing a fine tuning of the PCM.... go find someone who can tune your car.
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Old Jun 18, 2009 | 09:12 AM
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My 1998 does the same thing randomly. Wires, plugs, pcv and filters all done and it still has a slight lope at an idle at times. Quarter mile times are fine as well as fuel economy and zero oil consumption between changes. When I change the cam it will have a reason to lope!
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Old Jun 18, 2009 | 09:45 AM
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Same here. My idle feels like I have a cam installed. It has gotten a little worse when I installed 60 lb/hr injectors. I have a wide band O2 and my car runs on the rich side (about 14.2 AFR).
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Old Jun 18, 2009 | 12:25 PM
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Have you pulled the codes yet?
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Old Jun 19, 2009 | 12:50 AM
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Originally Posted by GMV8
My 1998 does the same thing randomly. Wires, plugs, pcv and filters all done and it still has a slight lope at an idle at times. Quarter mile times are fine as well as fuel economy and zero oil consumption between changes. When I change the cam it will have a reason to lope!
Seafoam may be the cure. It worked very well for me. Idle is bang on now.
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