Well, if you aren't getting any check engine lights, then I'm going to guess that your sensors are ok. It might be a good idea to try a new computer (PCU or ECM). They're fairly cheap (about 60 bucks) and they should be replaced after several years, just for preventative maintenance measures. You have to be certain to match the exact computer with your engine.... ie dont use a z24 computer for a regular 4 cyl cavalier. I've seen computers go on Z24's before and it baffles mechanics. Good luck dude.