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gomi_otaku
gomi_otaku, VW Technician
Category: VW
Satisfied Customers: 3459
Experience:  VW FastTrack '00-'01, VW Academy Chicago and Seattle '00-present, VW Certified
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I have a 92 GTI 8v with Digifant II that has intermittent

Customer Question

I have a 92 GTI 8v with Digifant II that has intermittent symptoms. The air flow meter starts creeping up causing it to run rich and sputter, especially bad at idle. Sometimes it will stall. If I unplug the CTS or O2 and put it in open loop it returns to a suitable position for its throttle opening, but still runs slightly rich because it thinks it's -40 degrees so I get bad gas mileage. The AFM is a gives proper resistance values at all openings and does not bind. I don't understand why it would be opening up too much physically, but when an electrical change is made (open loop) it snaps back into place? It used to happen about 1 or 2 days a month but for the last two months it has occurred every day, so I have been leaving the CTS unplugged and giving it some throttle for warm starts. I don't have a catalytic converter so I am not damaging anything by running in open loop mode.
Submitted: 1 year ago.
Category: VW
Customer: replied 1 year ago.
https://www.youtube.com/watch?v=VrMed-RFIJ0 Video of the problem
Expert:  gomi_otaku replied 1 year ago.

Are you sure that both of your fuel pumps are OK? I had a failing outer pump, and it would run bad intermittently.

Just brainstorming the situation- if it is running lean due to fuel starvation, the engine may race- but setting it back to default by pulling the ECT may allow it to run normal because of the rich mixture.

Try pulling the connector on your in-tank pump in the trunk, and see if it still runs (you should have enough of a reserve in the outer reservoir for the outer pump to run if it does run.

Customer: replied 1 year ago.
I will try in the morning but when it is running badly it is definitely running rich. The exhaust smells like spilled gasoline when it is acting up. And I still don't understand why the AFM would be creeping upwards. If it isn't drawing in more air how is the flap moving more? And if it actually is drawing in more air then why is the mixture so rich? Would a severe cut in ignition timing have anything to do with this?
Expert:  gomi_otaku replied 1 year ago.

If you already have a new ECT sensor, have you tried replacing the front O2? That should be the only other thing that would throw the system off really rich, that could be corrected by putting it back into open loop. If it were a mechanical issue causing a rich condition (free flowing injectors, burning oil, etc) I wouldn't think you would be able to reset it.

Customer: replied 1 year ago.
I unplugged the in tank fuel pump and ran it to warm up in order to test the O2 sensor (only one on my car). It ran fine for about 2 minutes then started sputtering like it does, so I unplugged the CTS to bring it up to temperature so it could idle smoothly. Unplugging the in tank fuel pump seemed to make no difference. Once it was up to temperature I turned off the car and plugged the pump back in to test the O2 sensor. I had an analogue voltmeter which didn't seem to be sensitive enough to test it. The third time I restarted the car it was running normally. I drove around for about an hour and it ran normally the whole time, I picked up a digital voltmeter to test the sensor. It seems like the O2 sensor isn't producing much voltage at all, which was strange because it was running fine after it failed the test and I plugged it back in. I should also note that yesterday when I unplugged the O2 sensor it was experiencing the symptoms of the problem, usually it does not though. I don't drive around with the O2 unplugged because the revs hang for a long time between shifts. The O2 sensor is very expensive and I am not sure it is the culprit here.
Expert:  gomi_otaku replied 1 year ago.

It's hard to test an O2 sensor, since the voltage it produces is pretty low. It should fluctuate, up to about half a volt normally.