Recently on my 126 the idle has increased by maybe 50-100 rpm (bareley noiticable on the tach) but enough to make the gears jump harder while changing from R to D etc. Sometimes when I have AC running then shut it off the idle is not the same but gets back to normal quickly but now its been 2 days. It happened pretty much overnight cause in the morning it was like that and still is now.

It is not the idle modulator (black box) cause when I had that go last yr it was all the way up to 1800 rpm.

Where should I look? Again its a slight increase but not too noticeable on the tach....though its noticeable while at standstill in D at a light.

thanks

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99 C43
98 S420
99 C230K
01 C240

If you truly wish to look, you should view the idle valve command with either or both an ammeter and a scope or duty-cycle gauge.

You didn't state a year so hard to give advise as to what to look for. Your statement that it went to 1800 means you probably have an 85 or older K-jet w/lambda. You are going have to get over the concept that the failure of a control module causes exactly "X" condition. Just ain't the way it works, lotta "grey" in this trade (as opposed to black or white).

The common reason for inability to control idle speed is an air leak. The module only can drive the early valves closed at 70% duty cycle. if its doing that either the valve won't close or air is coming from elsewhere.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

1983 380 sel......it went to 1800 last year when the idle box was at fault!

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99 C43
98 S420
99 C230K
01 C240

This thread is sinking faster than titanic......anyone?

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99 C43
98 S420
99 C230K
01 C240