I have the M110 2.8L dohc six in my '84 G-wagen. The engine runs way to fast at cold idle, sometimes nearly 2000 rpm. I know that there are a couple of parts that could be responsible. The warm up compensator, which is painfully expensive, and the aux air valve. I have checked to make sure that the throttle plate is closed all the way. I have adjusted the idle speed screw in all the way. If the engine is run up to operating temp, the idle stays up. If it is warmed up then shut off for a few minutes, the idle will come down. Am I correct in that the WUC controls the opening and closing of the aux air valve? Does it control anything else? I was told it uses a bi-mettallic strip as a temp gauge, is this true? So do I have a faulty WUC that is sending bad signals to the aux air valve, or a slow reacting air valve that doesn't respond to the WUC? Help! I can't stand the high idle and it certainly isn't good for the transmission

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1995 G320
1984 280GE
1971 Unimog 416

cold start TIMER / temp unit?

what injection are you running D ject L jet?

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C140 420 CL
W114 280CE pimpmobile
W114 250/8 Hillclimber with M110 and bike carbs - got any hot cams?

It is L-Jet. I was advised to first remove the intake and replace all of the vacuum lines.

Sounds like the WUC controls fuel pressure and can lead to rich/lean conditions. Mine is more of an air leak. I will also try and clean up the aux air valve while I have it apart.

I am now waiting for my parts catalogue on CD to make a list

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1995 G320
1984 280GE
1971 Unimog 416

The only L-jet, MB ever used, was the LH used in 119 v8s and the first year (1992) electronic 104 injection.

What most 110 engine have is K-jet, with some US models having K-jet w/lambda. I presume what you are calling a WUC is the control pressure regulator. This has nothing to do with engine speed. It is used the vary the mixture for warm up and sudden acceleration. What you do need most likely is a new auxilary air valve. This valve has a wax bulb in it just like the thermostat that warms the motor. As the engine warms the bulb expands and opens the valve in a thermostat. In the aux air valve, as it expands, the airslide closes and the extra air needed for cold running is shut down.

Remember that engine speed is determined by the amount of air entering, not the amount of fuel. Any way that extra air gets in the motor will cause it to run faster. If you have the idle screw all the way in you either have vacuum leaks, a throttle that isn't closed, a bad aux air valve or too much timing or a combination of all of the above.

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

Thanks Steve,

You are corret, it is K-jet, I checked the manual.

Your comments agree with the mechanic I spoke to at the G dealer. He also mentioned a possible mixture adjustment. I haven't had the truck for more than a few weeks and I am just starting to get it sorted out.

I am going to remove the intake in order to replace all of the vacuum lines hiding under there. I will try to clean the air valve if it is at all servicable. I need to do a valve adjustment and set the idle mixture and check the timing. It also needs new plugs, wires, cap rotor. I seem to have my work cut out for me

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1995 G320
1984 280GE
1971 Unimog 416