I am new to this list and have recently bought a Cavalier 2.0 16v SRI Ecotec. I got this car so I can have some reasonable transport for a year while I pay off my loan.
I have been quite happy with the car apart from its not quite as quick as I thought but thats mainly because you have to rev them quite high, apart from that I think the car drives really well and I am pleasantly suprised how good the suspension is.
The car has done 111k and apparently had a new camshaft sensor about 10k ago, I know the idle control valve is very dirty and I will clean it out in the next couple of weeks.
There is something that is really baffling me, when I jump in the car in the morning its starts ok and the engine management light goes out immediatley, sometimes the oil pressure light takes a few seconds but it seems ok. The problem arrises when I have been driving the car for longer than about 1/2 hour and I stop the car and return to it within approx 1hour, when starting it the engine management light comes on and stays on, also it becomes a little more hesitant and not as smooth when pulling away. If I leave the car for a few hours and go back then the engine management light will disappear immediately.
Your problem sounds bit like a faulty CTS (coolant temp sensor). This is bit like a electronic version of a choke. The ECU needs to know the temperture of the coolant water inside the block. If the engine is really hot or cold, it has starting problems.