gidpor:

I cured the rough idle/unstable idle hot on my mother's 300E by replacing all the rubber vacuum lines and the rubber hoses from the idle valve to the intake and fuel distributor. All of them were bad, and caused unstable idle mixture problems.

A dirty idle valve will do the same thing -- it gets stuck and won't control the idle properly.

The rubber hoses are standard vacuum line -- take a piece into the auto parts store and get about 3 or 4 ft, then replace all of the short one, between the intake manifold and all the sensors, etc. The main part of the lines are plastic.

The idle valve is under the air cleaner (remove the lower half -- three screws, one in front, one at the rear, one on the side by the fender). The idle valve is held on by two large screws and has a 3/4" or so hose on each side. Single electrical connector, two pins.

The hoses on my idle valve were rock hard and loose on the barbs. The one between the fuel distributor and valve was easy to change, the other one is a bear. The cold start valve plugs into it, and the connection is very difficult to reach from above. Had to use a big screwdriver and a long pair of pliers to force it on, and it has a clamp on it. Much easier from below with the belly pan off.

You can remove the idle control valve and flush the hose connection part with carburater cleaner-- spray some in, shake, it, then dump it out. Repeat until clean. It usually only gets crudded up when the hoses leak.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!