Rough idle then smooths out
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!