I have a 1995 m3 s50 and when I start it up cold or after ive even been driving for awhile it chuggs and check engine light comes on. After letting it warm up for a few it seems to drive fine and no real loss of power, But when you come to a stop it starts to chugg again light comes on and the smell of eggs comes out of nowhere. stop test said 1221 but i just replaced the o2 sensor little over a month ago. After I had installed the o2 sensor the car was running fine. Passed emissions no check engine lights ran great for 3 weeks then back to the same poor idle and lights on. So if you read this and feel like giving me some advise lets hear it.. Thanks