Danno

Hmm, when you disconnect the O2-sensor, the DME no longer uses closed-loop feedback. This makes it do a straight look-up off the fuel-maps using RPM vs. load (AFM-voltage). This will tend to be richer than ideal, so the O2-sensor will read rich. Probably 0.90v or higher depending upon how rich the mixture is. This will change as you drive the car because the actual airflow will be different than the fuel that's pre-programmed in the chips (they're close but not spot-on, thus requiring the O2-sensor feedback).

To check the air-flow meter voltages, tap in to DME line#7 near the DME connector somewhere. It's a small green wire with red-stripe. Measure + voltage there with reference to ground anywhere. Have an assistant slowly open and close the AFM flapper door by hand. It should range from 0.25v fully closed to 4.60v fully open. The voltages should increase smoothly as the door opens. Shouldn't be any sudden jumps or drops.

Then test the car while monitoring the voltage on this line. At idle, it should be about 0.82-0.89v. Drive the car and notice what happens to the voltage as you get the stumble. If the voltages stay steady or increase smoothly, then the AFM is fine.

LR45

Great info, but one question. Where is the DME located
Thanks for the help
86 944 N/A

Magnus

Some info about fixing the AFM, worked for me.
<a href="http://w1.132.telia.com/~u13204456/motronic.htm" target="_blank">http://w1.132.telia.com/~u13204456/motronic.htm</a>
(scroll down for english if you don't read the universal language swedish )

The output voltage range for N/A and turbo cars are different, I think it is 0.15V - 9V or something for N/A cars.

//Magnus

instigator

i had a similar problem and it turned out to be the idle air valve sticking open. hope this helps

Danno

"Where is the DME located"]

Check out the "AutoThority Chips": installation procedure on my <a href="http://members.rennlist.com/951_racerx" target="_blank">951 RacerX website</a> for photos of where the DME is located and how to get to it.