For years I've been getting a check engine light on with a Code 4 from the diagnostic module.

(Code 4: Air injection system faulty hot film mass air flow sensor with hot wire.)

Pins 8 and 14 of the diagnostic module were checked and show no faults.

A few years back I replaced the air mass meter hoping the fault would go away... it didn't.

Otherwise, the car runs fine with good gas mileage. What could be causing this fault?

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95 E320 Cabriolet, 169K