As the weather begins to chill again here in the northeast, a familiar and annoying idle 'dip' occurs when my car is cold. My Z3 starts without any problem and runs fine until it gets about a quarter of the way warm. Then, when at idle, the rev's drop suddenly from 800 rpm to 300 rpm just as though you were to turn off the key. The engine then catches itself and the rpm's return to a normal and smooth 800 rpm for about 30 seconds before it happens again. Its almost as though the car is testing to disengage the automatic choke, realizes its not warm enough yet as the rev's dip, and re-engages.
This only happens at idle (at a light by my apartment or something) when the car is very cold, and only once did the car stall completely while at a light on a very very cold day last winter. When it gets about 3/4 of the way to normal operating temperature it runs as smoothly as ever. Also, it never happens above 50 degrees.
Any thoughts? My mechanic thought it might be a fault in the electricals or a faulty oxygen sensor, but that doesn't seem to explain the fact that it only happens when cold and at very set intervals (I haven't timed it, but its about every thirty seconds). Does this happen to anybody else?
This only happens at idle (at a light by my apartment or something) when the car is very cold, and only once did the car stall completely while at a light on a very very cold day last winter. When it gets about 3/4 of the way to normal operating temperature it runs as smoothly as ever. Also, it never happens above 50 degrees.
Any thoughts? My mechanic thought it might be a fault in the electricals or a faulty oxygen sensor, but that doesn't seem to explain the fact that it only happens when cold and at very set intervals (I haven't timed it, but its about every thirty seconds). Does this happen to anybody else?
