I'm guessing you have Motronic 1.1... (archive)

The fact that you have an '88 tells me you have Motronic 1.1 ignition & injection control. You should have a 20-pin diagnostic connector under the hood. If you have a 15-pin connector, you have Motronic 1.0, which has a separate idle speed control unit.

If you have Motronic 1.1, it unfortunately looks like you have a defective MCU. You could try disconnecting the battery for a little while, then reconnecting it.

If you have Motronic 1.0, the idle speed control unit is likely the problem. You might try inspecting & cleaning fuse #6. Also try reseating the large connector on the engine side of the fusebox, and the two-pin connector against the firewall below the Motronic unit. These two connectors supply power to the idle speed control unit.

Good luck- HTH.

My 88 528e idles fairly normally (600-800) during normal daytime driving. Here's the problem. When I turn on the headlights when the car is in neutral or park, there is no effect on the idle, this is what I would expect. When the car is in gear (like at a stop light) and and the headlights are on the idle drops to below 500 to the point where it barely runs. I have to turn on the AC, which jumps up the idle just enough to keep it running. When I start to move the engine still feels good (Ie. No missing or ruff running). If I turn my lights off everything goes back to normal...of course turning off the lights at night doesn't work vewy well.

Any suggestions about why this is happening would be very much apweciated. :)

James.

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