2001 Cavalier Z-24 Stalling and high idle..HELP

2001 Cavalier Z-24 Stalling and high idle..HELP Have a 2001 Z-24 Cavalier. Been having problems for about 8 months now. Occasionally, the car will stall when you either press in the clutch for a couple of seconds while the car is going.......or when the car comes to a complete stop. I have replaced every sensor I could personally replace such as the MAF, IAT, IAC and TPS sensor. I've cleaned the throttle body plate really good. Before it started stalling (and it only does this maybe once every week or sometimes once every two weeks), it had a high idle....but only sometimes. Even now, occasionally, the idling will be really high....as high as 2000 RPM and will not go down for like 10 minutes. This happened today when I was driving home. It was about 82 degrees outside and when I cranked it over, the idling was up about 1800. I let it idle for like 5 minutes and it was STILL idling high. Decided that I might as well start driving since it wasn't going to go down anytime soon. I live 10 minutes away from where I was at, so it finally started to idle right a few mins before I got home. Very stumped with this problem, but I'm ready to pack it in with this POS. Had it to the dealer several times. They couldn't find anything wrong with it but decided to replaced the PCM anyway (to no avail). Whenever I take it to a shop, it doesn't really act up. No codes are stored in the computer. One add'l thing I've noted is that the car will use between 2 and 3 quarts of oil every 3000 miles. Don't notice blue smoke, but sometimes smell burning plastic smell (oil burning in cat?). Don't know if the oil consumption is related or separate. Any help is MUCH appreciated and might just save my sanity! :screwy