I have been trying to trace the awful idle on my 560sel.Once past 1500RPM it is as smooth as silk.My fuel economy guage seems to be off towards the red a little at idle.Never sits pegged to the left unless I am at highway speed and easy on the gas.Is this fuel economy guage reading a possible indication of a vaccum leak and were on this vehicle does it attatch to the manifold.I have searched everywhere for a vaccum leak and cannot find one.Also my milage is lousy!

Sounds like a vacuum leak to me. The faster your engine runs, the less effect a leak has on it due to the amount of air going through the engine.

Your vac leak could be on the inside - switching my climate control from off to econ pegs the needle all the way to the left instead of being 1/8" over.

Might check your vacuum reservoir as well. An idle that's real bad is usually a sizeable leak - try unplugging the vac line from brake the booster and plugging it (the line) with your finger and see if it smooths out any. Make sure to check for cracking on the hoses around your idle control and to check the idle control itself.

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A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.

Were is the vaccum resevior?

Try spraying some brake cleaner around the injectors area...if the idle jumps on it's own, you probably need new injector seals, and/or distribution hoses (not sure of the proper name). I would take the air cleaner off and inspect ALL vac lines for cracks, etc...

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

Already did that and nothing.

If you have a vac line to the transmission, check that too.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma

Some more info. When cold the economy guage is farther to the red than when warm and as it warms up it moves back to the left but not all the way.If I put it in nuetral it will go all the way to the left but when I put back in gear it moves to the right again.

Does it make a difference if you turn the A/C on or off?

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma

That's normal. As your engine warms up, metal expands, and the clearances between moving parts decreases, creating more vacuum.

As far as putting it in gear and having it move - mine does that too, but I think I have a bad/leaking vacuum modulator. I have slightly "hard" shifts going from park or neutral to a forward or reverse gear - it basically shifts the whole car either nose down (forward gear) or nose up (reverse) - and that's with a decently smooth idle.

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A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.

I have the same problem when shifting and sometimes it takes a while to get from park or nuetral to forward or reverse.
And it does move when the a/c is on.

two main places to check, the vacuum line on the back of the intake manifold and the four way vacuum connector by the second firewall. Mine used to start and idle like crap when on of those had a vacuum leak.

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual

What do you mean by the second firewall?

Didn't realize ecpnomy guage was that diagnostically important.
I can't remember ever seeing my EG all the way left

Having issues also & this thread raises interesting points.

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83 500 SEC Euro 198K