High Idle?

[bryceslu]

As far as I know its stock except Lid and TD's without headers, and a GM LS1 stock replacement about 30K miles ago (previous owner). I have no idea if anything else would be done that I cant see. I think my idle is too high when cruising

When I pull it out of gear, it is m6, the revs drop to and stay at 1200-1300 or drop to 1000 until I come to a stop, and maybe go back to 700ish. this seems a little too high until I stop. I am thinking that there may have been a tune before the engine was replaced, again I have no way of knowing what was done before me.

Anybody have an idea here, is this common/correct?

My exhaust will also backfire when I rev it past about 3K and pull it out of gear, even when the car is up to running temps. again...seems like it might be set to run a little rich?

Thanks for any input.

[JunkyardZ]

I think that on most manuals the computer will keep the idle set a little higher untill the vehicle comes to a stop. Off the top of my head I can't remember why but I know it makes sense, if I think of the reason I will let you know. Seems like my 94 that was an M6 did that. As for the backfiring...is it just the exhaust rumbling, like when you use engine braking to slow the car or is it an actual backfire?

[bryceslu]

Its not really a rumble. definitly a popping sound...but I dont run any mufflers. definitly more of a backfire.

[pajeff02]

Check for a rotted PCV hose that is allowing air into your intake, or anything else that may be the source of a vacuum leak.

[Cutlass]

^^^ Yep.
That exact same high idle thing has happened to me twice now. First time was a throttle body problem (see this thread) and the second time was a rotted PCV hose