2005 8.1L

[dewfpo]

Truck now has 2,000 miles on it. It has always had a fairly rough idle when in neutral. In fact it's so rough that I shut it off if I stop at the bank or fast food drive though, or at the mailbox. In drive it's smooth. A/C on or off doesn't matter.

 

The roughness is a shake like a random cylinder is dropping out. Not a consistent miss.

 

Different brands of gasoline or octane don't seem to make much difference. No MIL lit.

 

I haven't taken the truck in yet becasue nothing else is wrong with it and I have almost always had bad experiences taking my truck in to the dealer. Either's it's Normal for they botch something else up, so I'm conditioned to be hesitant.

 

I guess I'm just delaying the ineveitable but thought I'd ask.

 

Just wondered if anyone else with this engine is having a similar problem.

 

Thanks, DEWFPO

[2004GMC2500HD]

I have a 2004 GMC regular cab 4x4 with the 8.1 / Allison. It has 13,000 miles. It has had the exact same problem yours does since day one. I have no idea what it is, but you are not alone.

[dannyukonxl]

is it variable as in engine rpm?, cant say i have engine rpm rough idle, but when im in drive and lightly on the brakes so it creeps forward a little, it shakes a little bit like the engine is not balanced right or something, but the rpms are at 600 flat the entire time, wonderful engine though

[dewfpo]

The rough engine is only at idle in neutral(AC on or off), other than that the engine runs great, pulls strong.

 

DEWFPO

[Shaners]

That's a big motor that is idleing at very low RPM's. Even my old 6.0L would shake the radio antenna a bit at idle... but it was only turning 550-600 RPM's...

 

On the other hand, my buddy has an 8.1L in his 2500 Avalanche, and it has had to have several injectors replaced to help smoot out his engine... I think he did set off a missfire code in his computer though.

[Chevy Tough]

Interesting my 02 Silverado HD which has the 8.1 with the Allison does'nt have any rough idle that i notice, its a hauler when i haul.

[dewfpo]

Lucky you!

 

DEWFPO

[Chevy Tough]

 

yeah, i keep it maintainable, but i hope you find your problem

[8100 Power]

I have the rough idle to,(check sig) but mine could be b/c a need of tune up, im at 122,000 miles and counting.....

[Haulin' 8.1]

Try an injector flush and a Crankshaft Sensor Variation Relearn.

 

Vernon

[AmericanMuscle]

I've felt it before too. Mine normally doesn't do it, but I have had it do it a few times now. It's after the engine is warm and in neutral idling.

 

It feels like the rpm is dropping too low, but that doesn't appear to be whats happening. If I rev it a little bit, it usually quits.

 

'05 8.1L w/ 22k miles