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Old 01-12-2004, 11:57 PM
Posts: n/a
W126 neutral idle speed

Hi everyone, I have searched the archives and can't find a definite answer for this.

The car idles at 600rpm in any gear but in neutral it jumps to about 900-1000rpm which seems very high.

What do others have?

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Old 01-13-2004, 12:44 AM
Registered User
Join Date: Aug 2002
Location: La Quinta, CA
Posts: 271

I have an '86 560 SEL with 130K miles that does the same thing. Car runs great, gets good gas mileage, just seems to idle a bit high.
1986 560 SEL (159K miles)
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Old 01-13-2004, 07:16 AM
MikeTangas's Avatar
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Join Date: Apr 2000
Location: So. Cal
Posts: 4,430

Mine idles about 600 in gear and just about 800 in neutral/park. Check your rpm's using a separate tach, the dash tach can be off by a couple hundred rpm.
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon least its a diesel

Non illegitemae carborundum.
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Old 01-13-2004, 07:46 AM
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Join Date: Dec 2001
Location: LaPorte, IN
Posts: 400
My tach shows about 650-700 in idle, drops slightly in gear. Neutral was at about 900 prior to the chain rails breaking and subsequent restoration of the engine. Hard to know what reduced the idle--new chain and rails, valve guide seals, new fuel injectors and air distribution lines, plenum gaskets, left side head gasket and exhaust valves, or general cleaning of the engine.

If i had to pick one part of the work that MAY have affected idle speed, it would be replacing the vacuum connectors at the throttle body (under the intake manifold--no way they could have held a vacuum before. Mike Tangas documents these buggers very well in his 560sel accomplishments thread (almost a bible for 560 owners) but they are much easier to do with the intake off!!

The other strong possibility is the air distribution lines to the injectors, one of mine was cracked and that may have helped. I did NOT change or clean the cold start or idle control valves, though they were both removed and replaced. Best wishes.
Earl McLain
'02 C230 Kompressor
'89 560 SEL "Frau BlueCar" (retired April 2004)
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Old 01-13-2004, 01:20 PM
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Thanks guys. I have been suspecting a slight vaccuum leak as I have also been having an intermittent lumpy idle which comes and goes.

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Old 01-13-2004, 03:07 PM
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Join Date: Jan 2004
Posts: 6
I'm just guessing, but when you set the car in "drive" this will engage the clutch in the tranny, by means of oil pressure from the oil pump. the engine will then drop some in RPM. the idle speed on my 560 is also increasing and decreasing, I've read somewhere that this is normal, when the air condition compressor is engaging or disengaging by means of the magnetic clutch inside the compressor.

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