380sl idle high

[dvalente33]

Hello People, I won't be here long. I'm trying to help my 80 year old parents sell their 1985 380sl. It was just tuned up late summer and now the idle is real high around 1200. The car runs great except for the very high idle and it gets progressively higher the longer the car is on.

[rowdie]

If it starts immediately when cold and idles high I suspect the Idle Control Unit. PN 0025453332. Try twisting back and forth and see if the idle comes down. Not a sure fire test but sometimes works. If it does then either try reflowing the solder joints inside or replace.

[dvalente33]

Thank you for your response. It does start immediately and the car only has 60,000 miles on it. Only 2500 over the past 10 years. It was running horrible and the local benz dealership did a basic tune up and now it runs great except for the high idle which is all the time. Thanks again.I guess we will try the "twist and shout" with the icu.

[rowdie]

Where is the economy gauge needle at idle? If not pegged to the left they may have dislodged or broke some vacuum lines while doing the tune up.

[dvalente33]

I will locate the economy gage and see will the needle is. I'm guessing the gauge is probably staring me in the face as part of the instrument panel? I'm not to familiar with the car. Thank -You again

[rowdie]

It is in the left with fuel, oil and temp. It has a vacuum line attached.

[earl orchard]

my w126 380(m116 engine) also had a high idle problem search the forum(on one of my threads someone posted the test from the factory service manual you will need a multimeter ,very easy to do) for it there's lots of info about theses engines having a high idle, seems to be a common problem. IIRC the idle should be around 550rpm warmed up, around 750-900 cold. if the idle never drops i would bet its the idle control valve, a small silver tube on the front of the intake manifold. my engine would idle normally sometimes and other times it would idle high like yours without rime or reason, if it stays on high idle all the time i would bet its the idle control valve and not the module,both parts are the same price, about 200 bucks for an aftermarket one, about double or triple that for a mercedes one. very very easy to replace ether one.
and of course check for a any vacuum leaks
cheers
kenny

[dvalente33]

thank you for the help