Do I have a high idle?

[Christy]

Hi all,

New W126 420 SE owner here. Love the car, and couldn't be happier with it. I've been pouring over this forum getting very useful information on maintenance, fault finding etc. I need your help.
When I shift from Drive to Neutral or Park, the engine revs increase to approx 1000rpm. Shift back to Reverse or Drive and the revs drop to 600ish.
Do I have a high idle issue??

Christy.

 

[markjay]

600 when in gear sounds to me about right for any car.

I would expect it to be no more than 700-800 when in Park, though.

 

[Christy]

Yes, I'm happy with the idle speed when in gear with the brake pressed but 100rpm seems high to me too. So, where do I begin to fault find this issue????

 

[markjay]

Well as it's an SE it will have electronic fuel injection (aka EFI).. if it had a carburetor I could tell you what to do

Does is settle when the engine is hot?

But why is it an issue? The car only spends a few seconds idling in Park, once before you drive off and then again before you switch off. You don't take it out of gear at traffic lights, do you?

 

[Christy]

Well as it's an SE it will have electronic fuel injection (aka EFI).. if it had a carburetor I could tell you what to do

Does is settle when the engine is hot?

But why is it an issue? The car only spends a few seconds idling in Park, once before you drive off and then again before you switch off. You don't take it out of gear at traffic lights, do you?

No its not a big issue at all, but its not supposed to idle at 1000rpm either, so I'd rather fix it than let it be....

 

[slade1]

Leaking vacuum hose/pipe?

 

[Bert_W164]

Leaking vacuum hose/pipe?

This plus PCV pipe if your engine has one.

I had a idle of 1100rpm in park, changing the pcv sorted it, then I found a slight leak where intake manifold bolts were loose...in the interim I tightened them back up to spec, all of which sorted my idle issues and lean codes in Star

 

[190]

Did the W126 have the Bosch Ke injection which is an electronically assisted mechanical system, in which case the idle speed is set by a screw that adjusts the amount of air bypassing the throttle plate.