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1998 GMC Jimmy Rough idle at start

Tiny
COOPER1829
  • MEMBER
  • 1998 GMC JIMMY
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 226,500 MILES
What would cause a rough idle after sitting for a day or 2? After sitting, say over the weekend, it starts hard, after about 5 minutes or so of cranking it starts. Running very rough and the check engine light comes on.
After running for a while, 5 to 10, minutes it starts to smooth out then completely smooths out and runs great.
I drive about 175 miles a day with my Jimmy. Normally this only happens when sitting for a length of tiime, only when it gets real bad will the hard starting happen over night. The guy I have working on my truck said at one time it was injectors. I started using GM injector cleaner and the problem seems to go away. Then in a week or so I have to dump in another bottle. I've used the same gas from the same station for years and never had a problem before.
Thanks for your help.
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Tuesday, October 5th, 2010 AT 7:51 AM

5 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Check engine light on

Have the computer scanned for code/s-you have a problem within the engine management system that caused the CEL to turn on-This is your starting point of diagnosis, finding out what's going on
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Tuesday, October 5th, 2010 AT 9:29 AM
Tiny
COOPER1829
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  • 3 POSTS
I have had it checked, only one code comes up.#5 mis-fire.
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Tuesday, October 5th, 2010 AT 10:29 AM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Check no.5 sparkplug, compression and injector
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Tuesday, October 5th, 2010 AT 10:31 AM
Tiny
COOPER1829
  • MEMBER
  • 3 POSTS
Couldn't it be possible, considering after the engine warms and it smothes out it doesn't have any thing to do with the injector or the plug?
If it were a worn injector, or there wasn't enough pressure to pop the injector open completely or worn plugs (which I had replaced in the spring)this rough running would be happening all the time?
As I stated before, after it warms up, maybe 5 or 10 minutes it smoothes out and runs great. My MPG is realativly stable at (give or take) 19.

Is it possible, Fuel deposits or something to do with ethanol? This would explain why, when I use GM injector cleaner the problem sibsides for a week or so then reappears/ What do think?
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Tuesday, October 5th, 2010 AT 10:55 AM
Tiny
RASMATAZ
  • MECHANIC
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Do what I've suggested and then comeback with some results
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Tuesday, October 5th, 2010 AT 11:13 AM

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