2005 8.1L

dewfpo · May 6, 2005

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 · May 6, 2005

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 · May 7, 2005

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 · May 8, 2005

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

DEWFPO

Shaners · May 8, 2005

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.