1978 450 SEL High Idle 2000 RPM

[benreal]

I have just acquired a 1978 450 SEL and based on the records the motor has about 35k miles on it since a complete rebuild. It starts up and runs fine (wants to die if you give it gas when cold) once warm. It drives great but the idle is high at about 2000 RPM cold and 1700-1800 warm. Not sure where to start.

Vacuum? Is there an idle control of some sort that could be bad?

I don't see an idle adjustment and don't know these gas engines so I'm lost.

Thanks for any help!

-Mark

[flutes]

Mark what petrol are you running on?  This won't account for all of the high idle but running on regular unleaded instead of high octane will make my 450 idle almost disturbingly high (although not quite as high as that...)

[benreal]

Just put regular unleaded  in it. Its the same gas I use in my 450 SL and haven't seen an issue in that car but who knows . I took my hand vacuum pump and looked all over for a vacuum leak and found nothing. This is really strange...how do you adjust the idle on these things? 

[benzjarr]

Turn this  with a simple flat head screw driver ignore the stuff in red it irreverent to this post



Its under the air cleaner box in that general area

[flutes]

You should switch to high octane anyway - there have been a few posts about this recently.

[benreal]

Awesome I'll give that try tomorrow. Thanks guys!

[TJ 450]

Yep, you should look at the idle adjustment, but I think you may have an air/vacuum leak which is also making it run too lean when cold.

It would be an idea to check for any disconnected vacuum lines and possibly plug things up.

Tim

[benreal]

Well, I tried the idle screw and cranked it all the way, it dropped the idle 200 rpms . I guess I need to go over all the vacuum lines again. Not sure what else it could be...?

[s class]

Make sure there isn't any binding in the throttle linkages, or transmission linkage.  Also, check that these linkages haven't been adjusted so far as to prevent the throttle from closing completely at idle. 

[koan]

The Auxilary Air Valve (also known as air slide, idle up valve, idle speed control valve) is another possible cause of high idle.

Have a look at these threads, auxiliary air valve and Warm starting drama....

koan