A classically erratically idling M20!

[johnna]

Hello readers, first post!

I have a 1990 320i cabby. It is a later Motronic injection car (55 pin ecu).

Overall the car is superb and when warn runs as sweet as a nut. However when started from cold...........
........ the rev needle varies between 900 and 1300 revs in an up-down way. This disapears when warm and the car warms quite quickly. But it only warms to a point, it only warms to the black segment between halfway and one quarter from cold.

I'm thinking temp sender here. Should I change the blue or the brown?

I have tested my three pin idle air stabiliser valve and the voltages are okay, apart from one side prong to centre prong is reading ~5V instead of ~10V.

Been searching for that bloody seventh (cold start) injector everywhere.... thanks Haynes.....

The air flow meter seems fine though.

I was going to buy a stat today too, but decided not to, wish I had now.

What should I do?

[Simon]

Hi mate welcome to the zone, the blue temp sensor is for the ECU, the brown one is for the temp guage, the blue one would be the one you need to change, this can cause all sorts of running problems, especially when cold.

[Brianmoooore]

You won't find the seventh injector, there isn't one on your engine.
If your engine warms up quickly, and the temp doesn't drop off with the engine idling with the heater on, then the themostat is probably OK.
Anywhere in the middle black section is OK, as long as the needle is well clear of the blue and the red zones. The middle section of the dial is expanded, and only covers a few degrees.