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Discussion Starter #1
I have been reading all the w126 high idle problems and resolutions on this forum. Have tried all the following:
check all fuses and relays
check for vacuum leak
check and clean idle control valve
adjust idle control valve by pulling the core shaft outward a little bit
check and clean throttle body and linkage
on and on and on

pretty much tried everything I've read and learned on this forum....!

This morning I've decided to take out the idle control valve one more time and clean it......while the valve is out, I looked at the fat elbow rubber hose which connect the top end of ICV to the throttle body, and decided to shoot some carb cleaner to clear it....seems there is a check valve of some sort embedded inside this elbow rubber hose. After putting everything back together. The idle problem solved, my 560 purrs like a cat at 500-600 RMP.

Can't believe all it took was just a can of carb cleaner. I think my particular problem was that the check valve at the other end of this elbow hose was stopped up thus confused the ECM to trigger the high idle.

High idle problem has bothered me for quite a while on multiple W126s I have. Very glad this one turned out to be the dirty check valve. Next time I'll start with the fundamental....clean all hoses and valves before jumping into any quick assumptions. Happy motoring



91 560sel, 300sel X 3
89 560sel
03 s500
04 e500( P.O.S.) avoid at all cost
 

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'82 Euro 500SEL, '85 Euro 500SEC AMG WB Cabriolet,'86 Euro 500SEC RUF
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9,487 Posts
I have never seen a check valve in either elbow.
 

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Premium Member
1991 560 SEC 1994 E500 2014 E350 Cab
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7,029 Posts
news to me as well. Perhaps this is what some indy did to keep the previous owner coming back for more repairs. I bought a house once that had multiple holes cut in the cold air return, thus causing the system to suck unfiltered air into the coil. It wouldburn out every 2 years. I bought the house and fixed that, but it was deliberate on the old owner.
 

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Outstanding Contributor
1989 560SEC, 1989 560SEL, 1995 E420
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4,086 Posts
Maybe the "check valve" is that litte crossover tube that has one end pinched.

Looking at it from inside the elbow it could look like a valve designed to only let air go one way.
 

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'82 Euro 500SEL, '85 Euro 500SEC AMG WB Cabriolet,'86 Euro 500SEC RUF
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9,487 Posts
I thought about that too, but could not figure how cleaning that would effect the idle.
I almost bet there was a vacuum leak and when the ICV was put back it sealed the elbow.
I also wondered if the connector might have been plugged???
I would like to see pictures of the check valve.
 

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2004 Mercedes e320 Sport Wagon 73k miles w211
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39 Posts
ummm your my new hero... 3 years its been driving us nuts... new ivc, alternator, spark plugs, fuel pump, air sensor, oxygen sensor... and it just needed a spray of cleaner up the elbow tube.. thank you..
 
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