Last week Cadillac put a new engine in my ATS. When my wife picked it up the check engine light came on. The dealer then took the car back and informed us that a sensor hadn't been plugged in properly. We then picked tha car up again last night. My wife took it to work and when I asked her how the car was running she wasn't too pleased. She said it was hesitating and running rough. She said it was very jumpy and downshifting hard and all around running anything but smooth. I told her maybe it just needed to break in a bit because the engine is brand new. When she got home from work I washed the car and decided to take it for a spin to see how it was. I didn't get halfway out the driveway and the check engine light came on again. I still drove it and it was aweful! It hesitated then downshifted hard and jerked me all around. I then called Onstar for a diagnosis. They told me to bring it in for service as soon as possible because there is a malfunction in the ignition system. I'm starting to regret buying this car and feel that this may be just the begining of many many future problems. I couldn't imagine owning this car without bumper to bumper warranty. I'm thinking maybe Cadillac is just a Chevy with lipstick on it and expensive lipstick at that. This is the most expensive car my wife and I ever bought. Maybe we should have bought another Audi instead?