Lowered my idle speed some a few months back. The car starts at about the first mark up from zero on tachometer. It idles lower occasionally, and then the check engine light may come on and the lights (dash, headlights) dim a little. A light dose of gas pedal pressure increases the rpms by what seems 100 to 200 rpms and the check eng. light goes out and the lights brighten up.

The car, when warm, idles a little above the first mark on the tachometer. Next mark up from there is marked 1000 RPM. Does anyone know if the first short mark is 500 RMP? Seems reasonable, but it doesn't hurt to ask.

The car is my 1990 745T auto 204K miles. Thank you.

Hey Paul,



I think you're right about that mark corresponding with 500 RPM. I would not trust the tach that low on the scale to be really accurate. I think thats why the manuals suggest connecting a auxiliary tach when making idle adjustments. A 200 RPM change will make quite a difference in the way the car runs, and its hard to see on the tach on the instrument cluster. From what you've said, you may need to kick up the idle just a bit.


Regards, Jon 'Uncle Olaf'

Thank you Jon, 500 is what I figure, too. The car idles very quietly at that speed. The muffler and tailpipe have recent physical damage and the car still is quiet idling in the driveway. Thank you again for the post, sorry for the slow turn-around here.

Hey Paul,



Glad to be of help. No worries about the turnaround.


Cheers, Jon