My buddy has an '01 Suburban 2 wheel drive 5.3L with 102K on it. Trying to figure out what this thing is doing. On cold start it starts and idle seems to be okay until you put into gear. Then the rpm's drop, put it back into park, and they go up again. Need some help trying to figure this out. Would say it was fuel related, but seems kind of odd. Told him to run 3-5 bottles of injector cleaner through it and see if it helps, but I think it is something else.

Thanks,

 

Try cleaning the throttle body first. Turn the key on and hold gas pedal to the floor this will open the plates. Then use carb cleaner and a tooth brush to clean it out.

 

seafoam is your best friend.