It's a GM 4L60E and the problem is a temporary idle increase of up to 500 rpm when shifting from Park to Reverse. Sometimes it will increase when shifting from Park to Drive , from Drive to Park and just on start-up before the lever is touched.
So, maybe it's not even tranny-related. Vacuum problems?
But it is annoying and may be a symptom of something worst to come.
Any ideas?
Probably not the trans IMO. It sounds more like an idle control problem where the computer is having trouble handling the load change.
Yeah, don't really think it's the tranny, either.
The computer isn't throwing any codes so whatever the cause, it isn't serious enough to register - yet. But it sure is aggravating because the idle speed increase is temporary and then everything settles back to normal.
My first guess is the iac valve. But clean your throttle body where the throttle plate contacts the body. Gms can act a little funny when that gets gummed up, so start there cuz its free.
In reply to gearheadmb :
It may be premature, but thanks on the throttle plate heads-up.
Satisfying my curiosity that it wasn't a bum MAF sensor, I cranked the engine and pulled the four point connector on the sensor; it immediately died. I'm taking that as confirmation of a good, working sensor.
Then, I removed the throttle body cover and the hose connected to the MAF sensor then shot it with a liberal dose a fuel injector cleaner. I let it sit for a few minutes and paid particular attention to the plate and where it meets the side of the body. On start-up, I immediately got a CEL so I know the computer is working OK. I shot some more cleaner in the throttle body, disconnected the battery to clear the code, waited a few more minutes, reconnected all the bits and started it again.
No CEL, immediate start and none of the temporary surge when shifting from P to R, P to D, D to P, or R to P. All that was done in the driveway so it will have wait until tomorrow for a real test drive to see if it's a real, more permanent cure.
I need to get a PCV valve for the Prelude, anyway.
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