Rough idle then smooths out
10

Asked by Palmettofarmer Aug 13, 2015 at 02:58 PM about the 1999 GMC Sierra 2500 2 Dr SL 4WD Standard Cab LB HD

Question type: Maintenance & Repair

Thanks for any help.
I have a 1999 GMC Sierra SLT 2500 4X4 6.0
Gas engine.
When cranking I get a really rough idle to
almost shutting off. After 3-4 min, the
engine will go back to perfect idle.  I
replaced the fuel filter yesterday but it didn't
help this problem.  I installed a new fuel
pump 18 months ago. Service engine light
is on but according to Advance Auto, there
are no codes. Please help!

3 Answers
65,510

firebird338 answered 9 years ago

Clean throttle body and clean or replace Idle Air Control valve or mass air flow sensor depending on which one you have replace fuel filter if have not done soon a while. As fas as the check engine light make sure the gas cap is on tight or may need replacing.

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