3100 rought idle...chugging

[Guest]

Hey, I just got a 97 Lumina, it has the 3100 in it. It's not running right, keeps chugging and puttering and has no power. It sounded like the timing chain went to hell, but I took it apart and checked it, and everythings ok there. It's giving me these codes: 121 high, 122 low, 123 sensor A, 300 eng missfire, 121 (throttle postition sensor). If anyone knows what the codes mean, like sensor A? or has any ideas I'd love to hear it. Thanks.

[Guest]

Dsoen't seem to be the coils...any ideas??