Erratic idle speed

[bas]

I have a 1986 325i fitted with a Motronic fuel system.
At tickover, when warm, the idle speed fluctuates between 500 and 900 rev/min.
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 10 volts when connecting between centre cable and one outer cable. When connecting between centre cable and remaining outer cable I have no reading at all.
I cannot find anything regarding this valve or its plug on the Motronic System Wiring Diagram that I have.
Can anyone tell me what these three cables connect to and what might be the reason for the erratic idle speed.

 

[bichmgnt]

I don't know what the voltages are supposed to be but you might check the connection at the idls control computer in the glove box. Mine had the same symptoms and it was a broken wire in the plug at that computer.

Steve

 

[travis325is]

Could be your o2 sensor, just a thought.

 

[AutoXfreak]

Check out your computer, It should be under your glovebox, (or under the steering wheel on Right hand drive). If the last 3 digits are 153 ( I think... I need to check) any way those computers where known for faulty wiring/ construction. I check the numbers for you!

 

[bmwjnky]

Have you cleaned your throttle body blade? If not I would give that a try. I see it all the time at work where a coustomer will come in with an idle problem and 8 out of 10 times its just a dirty throttle body.