Recently bought a used 96 Grand Am 3.1 that has a weird problem. I am seeing -20 ignition timing on my ACTRON CP9180, but the car does have a lot of pep which doesn't make a lot of sense to me. Long term fuel trim number is -10. MAP sensor readings are 38 to 50 (100 = barometric pressure), and will decrease (higher vacuum) to 28 to 34 if you slowly open the throttle. Confirmed this with a vacuum guage: 17in. at idle, increases to 19-20 as the throttle is slowly opened. I do know that a low, steady vacuum reading can be caused by late ignition or late valve timing. Have cleaned the IAC and tested the TPS. Have no vacuum leaks. I am not sure if someone has been inside this motor or not. By the LTFT number and somewhat high O2 readings, the car is running rich. Once in a while it will set an O2 code, but other than that, there are no present codes set. The engine will also occasionally idle high (1,500 to 2,000 rpms) - particularly on cold start - and it won't slow down on its own, you have to shut the key off and restart it to get it to idle correctly. Is it possible that someone has replaced the timing set in this and got the gear one tooth off (retarded)? Is it a possible PCM problem? I thank any suggestions because I'm stumped and frustrated. I know this isn't a Chevy, but it is a GM product and I thought perhaps someone might have seen this problem before. I drive a 1997 Z-71 with almost 300,000 miles on it, so I am brand loyal. Bought this car as our daughter's first car and I'm trying to teach her about how cars work.