BMW 318/325/M3/525/535/M5 1989-1993 Repair Information



The idle speed is controlled with a motor operated rotary valve. The motor is double wound and can be driven in both directions. Power is supplied from the main DME relay anytime the ignition switch is ON . The control unit selects which of 2 ground circuits to complete, opening or closing the valve as required to maintain the programmed idle speed. Further idle speed control is accomplished through very fine ignition timing adjustments. This allows very fast idle speed control; turning on the air conditioner at idle will produce almost no momentary drop in idle speed.

Idle speed and idle CO cannot be adjusted or changed. If the either is incorrect and the valve works properly, look for a vacuum leak, clogged air cleaner or fuel injection problems. Adjusting any screws on the throttle body is unnecessary and will not change the idle speed or mixture. The DME unit will adjust for any changes made.