In Reply to: Not as if I know anything. posted by Thomas Meacham on April 03, 2001 at 14:29:15:
But knowing which engine would be a great help. And knowing the symptom you are trying to correct woulb be a bigger help. On the 3.5 l Six, the ECM monitors the RPM by reading the toothed damper wheel. The ECM reads the Temperature sensor on the thermostat housing and the status of the A/C unit to determine the correct RPM. The ECM corrects the RPM by opening or closing the ICV ( Idle Control Valve ). The ECM reads the Flapper Position and Air Temperature from the AFM ( Air Flow Meter ) to determine the duration of the injector pulse. The duration of the injector pulse comes from a predetermined set of values until the O2 sensor begins accurately reading the Oxygen Quantity in the exhaust. Once this begins, the injector pulse duration is corrected "Real Time" in response to the O2 sensor value.
The most effective assault on idle problems is to clean the ICV with Carb Cleaner. Hunt for Vacuum leaks. ( When I bought my car, all of the oil pan bolts were about 1/2 loose. ) Look for Bad Plug Wires. Buy the Bentley Manual. Don't adjust the AFM Idle Bypass Screw. Don't try to adjust the spring tension of the Flapper in the AFM. Run a Dose of Techtron ( or your Favorite ), then do it again, then Change the Oil.
Thomas Meacham 1988 735i 100,500 miles