I have searched for this problem and found a few things but I am hoping someone can provide me with some more help.

I have an 87 420sel that has started to have a high idle in park and nuetral - around 1,000RPM after it warms up. Once I shift into a gear, the idle drops to around 650 or so. When I first start the car, the idle starts out at around 750 and will slowly climb to 1000 as it warms up. When it is at the 750 mark (cold and in park) and I shift to R or D, the rpms will go up to 1000 and then back down to 650 (when in gear).

I have tried to re-solder the idle control unit and have also cleaned and lubed the control valve. I have voltage at the control valve of .8v with key in run and car off to around 4v as the car warms up.

I have also replaced the 10amp fuse in the overload protection relay. Does any one have any ideas of what to check or what they replced on their car to fix a similar problem to mine. I am leaning towards the control valve but I am tring to be close to 100% sure on it before spending the $150 for a new one.

I should also add that my SRS light stays on for about 20 seconds after I start the car, but does not come on after that. I don't know if this is related or not.

Thanks in advance,

Dave W
87 420sel 168K

Other posts regarding fast idle problems on older 126s say to check the vacumn lines. They get old and can crack or perhaps you will find a line that has come loose. Check 'em out.

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1986 560 SEL (159K miles)

...check the vacuum connectors on the throttle body under the intake manifold. Mine were crumbling, and new ones settled the idle down nicely. Mike Tangas' post titled "560sel accomplishments" does a great job describing the r & r of these.

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Earl McLain
'02 C230 Kompressor
'89 560 SEL "Frau BlueCar" (retired April 2004)

Thanks for the advice. I have sprayed card cleaner all around the lines, injectors, air tubes, etc without seeing any difference.

The rubber for the vac line that goes to the front of the throttle body (I think it was yellow and white) was a little loose and worn. I replaced it but there wasn't any noticable difference. If I apply vacuum to the line, should it hold preasure? Not sure what the line does once it enters the throttle body.

There are also two lines on the side of the throttle body (drivers side) towards the back. They appear to be ok, but I'm not sure of their purpose of if they should hold vacuum or not.

Thanks for the help. if anyone has a idle control valve they would like to sell, please let me know as I think this is my problem.

Thanks

Dave W

You did clean the idle control valve with carb cleaner also right?

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**A few Hondas etc... etc... Not Worth Mentioning**
83 Euro W126 380 sel Money Pit (Sold)
91 W124 300e 2.6. (Sold) 3.0 Motor is Much better!!
93 BMW E34 Touring Wagon (Sold) Sweet Car!!
91 300e (Just 200k with Ease.)Best car ever ???(Sold)
90 420sel (Black with Tan Interior) Best car ever!!!!!!!

Soaked it for two days, flushing it a few times then soaked it in wd-40 for around 8 hours. Seemed to help at first then went nack to it's high idle (1000RPM) in P and N.

I may pull it agian and soak on laquer thinner over night. I also need to test the ohm's on it.

Dave

For some reason I doubt it is your ICV, I have a very similar problem, I swiched ICV's with one from another car and it didn't help much. I just noticed the vacuum connection to my EGR is not connected to anything, I am trying to figure out where the heck it goes. I think that is the issue with my idle!! My behaviour is the exact same as yours, only mine is intermittent. Search posts on the ICV it has been discussed in many posts here!!

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**A few Hondas etc... etc... Not Worth Mentioning**
83 Euro W126 380 sel Money Pit (Sold)
91 W124 300e 2.6. (Sold) 3.0 Motor is Much better!!
93 BMW E34 Touring Wagon (Sold) Sweet Car!!
91 300e (Just 200k with Ease.)Best car ever ???(Sold)
90 420sel (Black with Tan Interior) Best car ever!!!!!!!

Sorry about bumping an old thread.

I have the EXACT same problem as dewakin, high idle when warm. Did you find the problem?

//f

420 SE

I can see how you could be confused.
The fuel return line should be attached to the regulator. which bolts to the fuel log. One hose (the top most one) goes to the engine vacuum.
The fuel line from the pump is the one that goes to the gas filter if you can see it. It connects directly to the fuel log.