How do you tell if you need an O2 sensor or a Mass Air Sensor. My 89 300e infrequently is hard to start and when it subsequently starts it missfires. When it has done this (twice) the check engine light illuminates. It has 113,000 miles, so maybe it needs both or even something else. Most of the time it runs fine. Any idea? Thanks in advance ------------------

My check engine light went on in my C36 last week or so. I took it back to Mb and they diagnosed it saying the MAS was out of range, but the car runs fine if not better. Hope this helps.

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.

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Benzmac:
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