B21 that won't idle when warm
 

I previously had a problem with the cold start, for which I eventually found the part responsible and replaced it, and now a few months later I seem to have a problem once the motor is warm. It is a B21 motor, injected, and once it becomes warm (and I am guessing the cold start system goes off-line) it won't idle. I have tried adjusting the idle screw to no effect. At the moment the only thing that makes the car drivable is tightening the throttle cable a little. The manual doesn't seem to have any suggestions, does anyone in here? It is something that has happened from one day till the next so I strongly suspect that something has suddenly stopped doing what it is supposed to.

Cheers

Angus

the symptoms you describe will have a different meaning depending on whether the engine has or hasn't got an O2 sensor and does or doesn't run under closed loop control.

But anyway the first thing I would look for is an air leak into the inlet manifold. One method of doing this is to use a flammable spray of some kind near potential leak points such as rubber joints, gaskets, hose connections etc. when you hit the leak, the idle speed picks up.


If there is an air leak this may be tolerated when the engine is cold for two reasons;

1) the mixture is rich anyway and
2) the amount of air going into the engine is quite large; the drag of cold oil etc in the engine means there is usually at least twice as much fuel being burned at idle on a cold engine vs a hot one.

The latter point means that the significance of any air leak becomes greter when the engine is hot.

cheers

Thanks Brucee

I gave it a liberal go with some starter spray and it made no noticeable change. I did however play with the idle a little more, while I was there, which did produce a result. It is back to idling as it should and everything is good. Thanks for your input, it was appreciated!