The 89 300E does not have a mass air flow sensor. It has a air plate position sensor. You should take it to a tech. It will save you money in the long run. The check engine lights seem to take experience to repair.

------------------
Benzmac:
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM