Pontiac Repair: high idle at start-up, throttle position sensor, air control valve

Question
i have a 99 Pontiac Montana (3.4L) base model. I just change all plugs, wires, all 3 coil packs and fuel filter. I was told I had a mis-fire and that is why I changed the above.  My question is, sometimes, not all the time my RPM's are high at start-up and sometimes it will go to normal if i shut the van off and restart. when i did my tune up i cleaned the throttle body with throttle cleaner and changed out the Idle Air Control Valve when i did this. the high rpm been happening for a while even before the tune up, do you have any suggestions?  van does not stall or anything but usually when this happens when I'm driving it will shift hard...please help!!

Answer
Hi Leo:

I think you have a few issues here. The hard shift is more then likley if it happens when it good and hot a transmission pressure cotrol solenoid going bad. it usually sets a p1811 trouble code in the engine computer. have the van scanned for codes at a big box auto parts store. As for the past idle it can be caused by a lot of things from a vacuum leak in one of the hoses to a bad throttle position sensor that will not re zero after a key off.You could have another sensor like an a/C pressure sensor or a fuel tank pressure sensor that is going bad some of the sensors are paired togehter with the throttle position sensor could be going bad and it effects the throttle position sensor.  with out seeing it I can't tell you for sure. good luck :-}