The ECM controls the idle speed whether in "Park" or in gear. Not like the old carb days.

I think revisiting the cleaning of the IAC or Idle Air Control as RacerX suggested in post #7... I think the IAC is either gunked up or is not working correctly...

On the throttle body, there is no scew visible. Since it is drive by wire, there is a electronic control of the butterfly that has metal clips keeping closed. That is where the wiring harness attaches. It looks sealed, and I did not open it. My wife drove the suburban all overtown yesterday and getting a little better. When it first starts, idles down, but when driving, let go of gas shift in to neutral, revs to 2500 rpm. When you come to a stop, then shift to nuetral, goes to about 1000 then drops to 600. When I first start it and idles down, now idles back down if I gas it for a moment and let go. Before, I would gas at low idle then it would go up then continue up. So again, seems to be getting a little better. Wondering if cleaning fluid got into the electical unit on side is the source.

Ok, well I m going to stick with stuck Idle Air Control Solenoid. How did you clean the throttle plate with no linkage to open the butterfly?

In the Ford MPFI systems the PCM set the Idle also, but they still put an adjustment screw for the throttle plate on the other side of the TPS sensor. It wasnt really for idle neither, more like to calibrate the butterfly during reassembly, especially on cars with cruise control.

Volvo had that drive by wire Throttle Assemblies in the early 2000s where the PCM would set the whole thing, problem was that the software could fail and then the car wouldnt start because the Throttle assembly could NOT interface with the PCM.

I removed the throttle body, and manually moved the butterfly, even though it it is controlled by the ecm, it is spring loaded to shut, When I removed it the second time to check it, it was in the closed position when off, it does not appear to hang up in any way. If I remove the air intake hose, with the key on the run position and engine off, would the butterfly activate acorrding to throttle position?

Looking at the chevy parts, I dont see a seperate air actuator valve for the 07 suburban. I believe it is part of the actual throttle body.

Just an update from my origional post, after driving i would say about 150 miles my idle has gone back to normal.

Thanks for all the input.

Thanks for the follow up:cool:

Good to know that something in this computer controlled truck works. ;)

Update also, mine has also returned to normal operation. It took a little longer and more miles than I would have though. Thanks.