I recently replaced the heater/ac blower motor in my 86 240dl. Now this was a time consuming job but after 5 hours or so it was complete and worked awsomely, except for one minor issue. I bought the part from fcpgrotton and installed it exactly as the old unit had been in by attaching the ground wire on the motor to the ground wire that I had cut off of the old unit (which remained firmly grounded to some mysterious location deep in the bowels of the beast). The only issue that I have is that when the car sits at idle and the fan is turned off (from a previously on position) the engine actually revs 2-300 rpms!. At first I thought this was in my imagination as I don't have a tach in the car, but it most definatley does this every single time. What is going on here? It will not do it if the engine is running at anything other than idle speed. I had guessed that the blower motor puts out some sort of RF interfearnace that the idle air control valve or the trottle position switch gets momentarily screwed up by, but this seems like a long shot. Otherwise I have no idea how these 2 issues can at all be related. All vaccume lines are in 100% condition in the dash and all accessories work...this is nuts. can anyone help?

Yes it is the A/C switch..If it is turned fully counterclockwise then you got a bad switch..Fix it or replace it from P&P... Or maybe it just likes the blower motor turned off,, and it is rewarding you with a few extra RPM"s..Who knows....

If you have Air check that is turned off (A/C knob FULLY counterclockwise) since having the A/C switch on will tell the ECU to raise the idle up a few hundred rpms. If it is off, check that the A/C switch does not have a broken micro-switch that is attached to it. That is what happened to my 82. I was able to crazy glue it back together. Also check that you did not put a wire back on the wrong terminal.