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In Reply to: Revs Drop Suddenly On Throtle Let Off?? posted by Aidan on March 12, 2000 at 07:18:11:
: Can anyone pin point the problem of sudden rev drop when taking your foot of the throttle it only seems to do this when driving and not whilst stand still and reving the engine.It makes for difficult driving as when you let off it all seems to shut down ,not cut out but drop to around 12-1400 revs from say 2000+
: Could it be the throtle motor?The BMW garage checked and in the fault memmory it showed faulty oxygen sensors.
: Aidan
: 850i '91----90k miles
Your engine uses two Motronic computer units for the engine management systems and one EML unit for control of the throttle servo motors. When this EML unit receives simultaneous signals that (1) the throttle position sender (foot pedal) is fully off, and (2) you are above 1500-1800 engine RPM, and (3) you are applying the brakes, it fully shuts off the fuel supply. It thinks you want to stop. The brake light switch is a dual element switch with one element operating the brake light and the other element providing information to the EML unit (and the Motronics). If this element is bad it can send a false signal indicating that you are stepping on the brake pedal, and if you then back off on the throttle, it then produces full shut-off. To test this, simply unplug the brake light switch connector and see if the symptom remains. This one drove me crazy for a while, but it turned out to be only a $6 problem. Good luck with it.
Regards,
Kerm Achterman
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