I had replaced the intake manifold on my lumina a few months ago. After everything was put back together, the engine would idle fast (around 1500 RPMs), but only if it was in park or neutral. Also, while the car is sitting still, either parked with the engine running or at a red light, the SES light comes on. Sometimes it goes out after a few minutes, sometimes it stays on until I turn the car off.

The other problem I've been having is with the transmission. Unless you are pressing the pedal to the floor, upshifts and downshifts are harsh and cause the entire car to vibrate. Its similar to if you tried to shift from first to fourth on a standard or waiting till just before the engine stalls out before downshifting. I changed the fluid and filter, even though everything looked clean and added a bottle of SeaFoam but that didn't help.

The only thing that did seem to help the transmission was actually washing the car. After rinsing what I believe was brake dust out of the front wheels then the brakes and throttle worked like new again and even though the shifts were a bit anemic, they didn't cause the whole car to vibrate. After a few days driving in the snow though, the grinding is getting progressivly worse again.

One other problem that I've had on and off. Sometimes the car will not start. It doesn't even try to crank, as if the battery was dead. Everything in the car works fine, stereo, lights, etc, but the car will not start. If I pull the ECM Batt fuse for about 15 seconds then the car starts right up...