Ive been trying to get my friends M20 running. Its a 1989 325ix. he had it at a shop who couldnt figure it out and asked if i could look at it. it runs stupid rich and when you give it gas lightly it has no response, but if you snap the throttle quickly it revs up but after fires. its running so rich that it fowls out the plugs after about 2 minutes of idling. What is strange is that the CEL comes on when you give it throttle and then it goes off again when you let off. I read the faults out with an old GT1 and its a fault for pin 7 at the DME for air flow meter short circuit to B+. ive checked all 4 wires to the DME from the air flow and even ran a second set of wires just hot and dirty to see if they were shorting out and nothing. i have swapped the air flow meter with 3 separate meters and swapped in 4 separate DMEs. i know they all are functioning parts as i install them in my car and it runs just fine. ive replaced all the injectors with rebuilt ones, replaced the fuel pressure regulator on the rail, replaced the cap and rotor and plug wires. checked and adjusted the valves, cleaned and adjusted the throttle sensor beneath the throttle, adjusted the throttle closed clearance, swapped another known good idle motor and replaced the NTC coolant temperature sensor. Swapped fuel pumps, replaced the fuel filter. This car is driving me nuts and im out of ideas at this point. Has anybody here heard of this weird on/off CEL issue? because im sure its related somehow to this.
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A few thoughts, there is a connector under the intake know to corrode. Pull that apart clean and check all the pins. Check the temperature sensor wires back to the DME. Same thing on the throttle position sensor. Make sure the O2 sensor is working.
Take a look at this file, one of the most comprehensive all in one place explanation of the M20 idle. It is for an E model but can give you an idea of how it all works together. http://www.verrill.com/car/e30_idlefaq.shtml
Add in your wiring diagram from here: http://wedophones.com/Manuals/BMW/2004 525i Manual - 1985 325E Coupe Manual -
I have had the connector under the manifold apart as that is the connector for the injector harness and it is clean. (i live in the desert so corrosion is unlikely anyways). Ive had the throttle position sensor swapped with an new one that has been cleaned. I had it running with and without the O2 sensor plugged in with no difference. I know that these cars will run just fine, if not better without the O2 sensor plugged in at all. i have performed resistance checks on all the wires previously, but i will check the temp and idle wiring again just in case.Comment
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pretty intersting issue, and nice diagnostics so far.
What happens when you operate the AFM on the bench, does the pin7 short to the B+ on the AFM?Comment
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