M635CSi slow return to ilde

[Hansniskatuki]

This happens when engine is at normal temp, revs stay approx 1200 quite a while. But eventually return to idle. TPS is adjusted, throttle linkage is moving freely.. Where to next?

[GazM3]

Have a look at the throttle cable itself as it can bind up at either end. It's not fun having a throttle jam open so if its dodgy at all replace it. If the TPS is clicking ok the only other thing that can lift revs is it accidentally going to cold start mode. Mine is disconnected so it idles abit grumpy for first min or so.

[mojocoggo]

A sticking idle control valve or vacuum leak can also cause this.

[Hansniskatuki]

A sticking idle control valve or vacuum leak can also cause this.

I don't have ICV and vacuum leaks have been eliminated, fingers crossed (new hoses etc..).. The cold start valve and temp/time switch are also new.

[Pod]

On RHD cars the lever which goes through the firewall can get sticky. A squirt of WD40 or similar should free it.

[Brucey]

A sticking idle control valve or vacuum leak can also cause this.

I don't have ICV and vacuum leaks have been eliminated, fingers crossed (new hoses etc..).. The cold start valve and temp/time switch are also new.

eh? No ICV? How so?

cheers

[Hansniskatuki]

Looong time, no see.. I have this, 13631272166 ADDITIONAL AIR SLIDE VALVE. And still same the problem, including some hesitation when revving from idle..

[Brucey]

that'll be your idle control valve then. It is just a different sort to normal with a different name.

Somehow there is too much air and too much fuel getting into the engine until the idle settles down. I am a bit suspicious of a sticky throttle/throttle cable, since if the TPS and the throttle were closing in the normal way, the overrun fuel cutoff would activate, which would cause the revs to dip once to a low level. A metered air leak of some kind in combination with the TPS being closed would cause the rpms to rise and stabilise below 1200rpm or cause the rpms to hunt as the overrun fuel cutoff cuts in again and again.

If the throttle linkage is sticky or the butterflies themselves are maladjusted or sticky, or there is a spring missing off the linkage, it is possible for some of the throttle butterflies to stay open longer than they should. This will cause the symptoms you see.

cheers