idle problem !!!

[EuroMike]

I have a 1989 325i fitted with a Motronic fuel system.
When cold, the idle speed fluctuates between 500 and 900 rpm; when warm seems to be OK.
I have tested the Idle Air Stabiliser Valve as described in the manual using an ohmmeter and it is OK.
On testing the three cable plug connected to the stabiliser valve I have 12 volts at the centre cable and 9.8 volts when connecting between centre cable and one outer cable. When connecting between centre cable and remaining outer cable I have 3.8 volts.
I tested the continuity on wiers betwin ECU and stabiliser valve, wiers are OK can anyone tell me if is a computer (ECU) problem?

Thanx Mike,

 

[Kether]

I've used this test on VW's to diagnose idle problems, and it should also work on BMW's since we're all one big happy Bosch EFI family:

With the car running, and cold, smack the idle air controller, and see if the idle changes. Next, give the AFM (MAF?) a good tap or two, and note any change. If there is any change when you thump either of these, they're bad or on their way out. Idle air controllers can sometimes be resurrected for a little while with a good thorough cleaning with carb cleaner.

Let me know how it works out!