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Poor acceleration and mileage, AMM bad? 700 1991

posted by  fladave on  Mon Aug 22 03:28 CST 2005
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last visit: Sat Mar 13 09:49 CST 2010
[RELATED]

Greetings all!

HISTORY: I have a 1991 740 Wagon with 158,000 miles. I bought the car used and don't know the history. When I purchased it the idle was really high and it threw code 2-3-2. After spending time reading the FAQ here, I managed to fix these problems:

Throttle linkage was horribly misadjusted; the linkage was acting as a throttle stop, the TPS sensor switch was never sensing closed throttle. Readjusted linkage and TPS sensor. Cleaned flame trap; was mostly plugged with gunk. Cleaned throttle body; it was very dirty. Now idle was smooth, but still threw a 2-3-2. Cleaned AMM using quick burst of carb cleaner followed by blowing out with canned air. Reset codes and no new code (get 1-1-1) for over a month.

PROBLEM: acceleration is terrible, and gas mileage is about 15mpg in mixed city/highway. At idle, in neutral, if I goose the throttle there is a 1/4 stumble before any response.

Highway-only mpg is much better, about 26mpg.

If I pull fuel pressure vac line idle picks up a bit, but not a huge change. Haven't tested with a pressure gauge or pulled return line to see if pressure regulator is working.

If I pull the AMM connector the car runs EXACTLY the same, except the check engine light comes on. So right away I suspect the AMM is bad.

I measured the resistance of the AMM with a digital ohmmeter; its 870 ohms. If I blow on the sensor I can get the resistance up to just over 1000 ohms, then it gradually falls back.

My AMM has only two wires. There is no part number on the black tube the AMM sensor is mounted in, but on the small blue square connector with two contacts, the numbers "1537 1" and "212-90" are stamped. This confuses the heck out of me; all the references I see mention more wires, and "212-90" seems like the wrong part number as I've found these part numbers:

740 8 Valve 1989-1992 Air Mass Meter (old part number 3517020, Bosch Number 0 986 280 101) NEW Bosch Number (0 280 212 016). $350 (yikes!!)

QUESTIONS:Do I need a new AMM?

Could I have the wrong AMM installed in this car?

I will conduct the "see if strong stream of fuel is coming from the return line" fuel test next.









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