[6Ljunkie]

Hey guys,
I have an 07 Silverado HD2500 6.0L with 190 000 km. Everything so far is running great except at idle, the rpm jumps between 500 and 650. I held a $ bill to the tailpipe and its flapping so I think it's misfiring. If I don't let it sit at idle for a few minutes when I start up, the truck jerks and I get momentary loss of power.
Additionally, I'm getting around 8 mpg. I'm taking it in this week, but I would like to have some ideas of what to expect before I get there...
Any ideas??

 

[SilverSurfer]

No codes or no CEL? There may be pending codes. I'd check for pending codes and look for an intake leak.

 

[Bck4more]

Im having the same issues I've replaced the throttle body and MAF still having issues

 

[6Ljunkie]

Would an intake leak necessarily effect gas mileage? I was thinking that fuel trim would correct it, or the leak would just become insignificant when the throttle is more open?

 

[davester3500]

depends on how bad the air leak is. exhaust manifold leaking also causes problems with maintaining fuel trim (check that all the bolts on the exhaust manifold are present).

as well, check that you are getting proper fuel pressure (right about 60 psi) at the rail, and that it doesn't drop significantly when you hit the gas (more than about 15 psi, and it should go right back up to the original value very quickly).