1974-450sl-idle problem ?'s

[norwichhouse]

Just bought a '74-450sl.Car hadn't been run in 2 years. Idles at about 1200 hot & cold. Drove it home and it runs well at highway speeds, but had to use neutral at traffic lights.Unable to locate manual.Tried ALLDATA, they only go back to 1982. Thanks for any help.
Frank

[psfred]

The idle speed is adjusted with the large slotted screw on the front of the engine -- there is a hose from the left valve cover to the idle speed screw, then a y-shaped hose to the intake manifold.

Fast idle is controlled by a thermal valve on the right side of the crossover passage at the front of the intake manifold, has a hose to the idle speed screw assembly. If the valve is stuck, you will have fast idle all the time (and the idle speed screw won't do anything). A quick blow with the side of a hammer sometimes frees that stuck valve up, cheaper than a new one.

I would expect to replace the idle hoses, particularly the y-shaped one as any leak after then idle speed screw will cause a fast idle.

Take a look at the Vintage forum, too -- lots of us crazies have D-Jet engines.

Peter

[norwichhouse]

Peter,
I'll try that when I get home. The old hammer trick works on Chev idle air valve too.
This is a one owner 100k car. Owner has put considerable $ in parts. I believed he used non MB labor after he reitred to Florida. I'm hoping it's just a matter of adjustments. Have 2 wires unhooked at fron of manifold. One appears to match connector on air cleaner nozzle. Can't find a connector for other wire. May be a testing circuit?
Really need to find manual for at least the engine.
Thanks,
Frank

[psfred]

The rectangular fitting is for the engine temp sensor, which should be in the intake manifold water passage near the front. The single wire is for the thermo/time switch for the cold start valve. You can run without the thermo/time switch, but you really need the temp sensor connected or it will run WAY rich!

Check the wires to the sensor in the air horn as well, it will run way rich if that one is dissconnected, too!

The idle may work better with both temp sensors connected... If the one in the water passage has been removed, you really should replace it before driving any distance.

Peter