Truck idling high too high and trans not shifting right
 

I have a 99 silverado 5.3 with the 4l60e trans. Stock internals just magnaflow exaust cai no cats. It will idle and shift fine but after a while the idle goes up to 700rpms in gear and 1000 at park. The trans wont shift right, it hangs gears and wont shift till i let off. Does the tps control shifting in these trucks? Could it be a IAC problem or a transmission problem. Does it more when engine is in closed loop at normal operating temps. No codes.Anyone got an idea before i start throwing money at it.

Mine has done the exact same thing. Doesn't always do it but when it does its after its warmed up. I have a built transmission and replaced the 5.3 with a 6.0L. No codes as well:hmmm:

I heard a contaminated MAF can cause this, oil from k&n filter. I would try to clean it with seafoam before you replace any parts. I would try it with mine and let you know but im waiting for my pcm to get retuned.

Get some contact cleaner to clean the maf, pull the t/b off and give it a good cleaning with some carb cleaner. You can also pull out the iac and clean the whole passage with a tooth brush. Good time to do the coolent hose bipass too.

Pull the battery cable for 30 minutes and see if that helps.

Thanks for the replies. I will try that and see if that helps. Nobody thinks its a sensor problem right? Cause it would throw a code?

It sounds like it may be a vacuum leak to me. That explains the high idle anyways. Not sure how that could affect the transmission shift, unless the MAP signal has something to do with it.

I would guess the throttle position sensor could cause it but I would try cleaning the maf first. I goggled it earlier and that's what worked for most, the oil from aftermarket filters a screw with it.

Yes, TPS can do this also.

I agree, as mentioned I'd start with cleaning the MAF and Throttle Body, cheapest, easiest place to start, and may very well cure your problem.