1998 BMW 318

Electrical problem
1998 BMW 318 4 cyl Two Wheel Drive Manual 140, 00 miles

Bought this car in 2002 w/ 70,000 miles on it. The seller said there was a problem w/ the check engine light and he thought it was related to the gas cap being too tight.
In order to pass NH inspection I had to make sure the check engine light was off. Several sensors were replaced, the light went off and stayed off for about 2 weeks.
We moved to NM and the same problem occurred re registering the car in Albuquerque because of emission standards. Some more sensors were replaced, the light went out for 4 days.
It's now that time again to register the car again and I would like a permanent solution to this problem. Help, please.
Dogmom 02
September 20, 2010.

Which sensors?

Dr. Hagerty
Sep 21, 2010.