unstable idle speed

I have a 1989 BMW 318i with M40 engine. The idle speed is erractic. Any time I start the engine,the engine idle speed becomes unstable in less than a minute. It swings for a while, stabilises for a split second then swings and sometimes stalls.

When driving it is fine but when I come to a stop, the idle speed oscillates around 750rpm and then dies sometimes. Some time at low speed, the car surges forward.

I took the car to mechanic who cleaned the idle control valve. when he refitted it, the idle speed jumped to about 1500rpm from 700rpm. So the mechanic reduced the idle speed to 600rpm. The problem did not go away.

Recently, with the engine at idle of 700rpm, I removed the disconnected the wires to the ICV(idle control valve) and the speed went to about 1500rpm. I thought the speed will settle at 1500rpm since ICV was fully opened but rather speed kept on swinging.

Does it mean that ICV is not the cause of the erractic idle speed
If ICV is fine then could it be something else, like clogged fuel filter
Or throttle positioner problem.

I would appreciate help from you guys in fixing this problem which has been with me for 2 years. Even my wife does not want to drive this car any more because of this problem.

Have you tried replacing the o2 sensor(s)?

No, I have not replaced the o2 sensor since I bought the car from another guy in 1999.

Is there a way I can check its functionality?

Did you fix it man? I am having same sympthoms on my 320i e36 (m52). Feedback will be highly appreciated. Thanks.

I'm having similar problem lately on my 2000 BMW 328i. Has anyone figured out the problem?

Every issue I have had with unstable or erratic idle came back to the Idle Control Valve, many times disoconnecting the electrical lead, removing the hose, and cleaning the valve with Throttle Body Cleaner will solve the problem.

cam shaf positioning sensor, maf, erratic fuel sending unit could be one of those also