hmm...need help...new idling problem. 86 300E
 

Damn this is the 3rd idling problem this year...I need help this is driving me crazy.

Idle problems this year and it's solution
1. Coil
2. MAF and O2 sensor
3. ??? (Car was running fine. I've been cutting down on my driving since gas prices have been creeping up. My car will sometimes sit in the garage for 3-4days before I take it out for a spin. Now my car has a stumbling problem at idle. Otherwise it's fine as long you're stepping on the gas. It starts fine. Idle is rough in all gears, but really bad in drive or reverse. I asked my mechanic and he said something about vapors being in the line...he wants me to take it in. Can this be the fuel pressure regulator? I'd like to try to solve this myself before taking it in. What are the signs of a failing fuel pressure regulator?)

The following have been replaced with new part...along with the 3 above
Spark plugs/wires/distributer/rotor
OVP
alternator
Temp sensor
Fuel pump/filter

Engine mounts and idle control valve hoses are my first guess, these are very typical problems on that car at this age. Examine all the vac line rubber connectors and hoses, too, likely they are all rotten or rock hard and leaking either way -- this will give you terrible idle and serious throttle lag.

The steel insert on the bottom of the engine mounts must be visible, and the upper hemispherical part must be at least 1" from the frame. Any flatter than that, or oily residue on the frame, and they've ruptured. Engine will vibrate horribly since it's sitting now on a pair of undamped springs instead of shock absorbers!

Peter

Thanks Peter for your opinion. I don't think it's the engine mounts. It's not a vibration issue, but rather a stumbling rough idle.

ICV hoses is a possiblity...so are the vac lines.

With the Fuel Pressure Regulator costing well over $100, it looks like I'll spend less just taking it in to the MB mechanic. I've already changed all of the little routine maintance "stuff", I'm not going to worry about being charged $$$$ for simple things like replacing the spark plugs and filters.

You will need to have the pressure and differential pressure check on the fuel distributor before condeming the regulator.

Rough idle with normal operation off idle is either the throttle position switch or a vac leak nearly all the time -- failures of the pressure regulator or fuel distributor are almost never idle only.

Vac lines are a good place to start -- also, I'd check the fuel pump relay -- if it's hot, replace it. This cured most of the rough idle on my TE.

And, it could always be a dribbling injector -- this will cause one cylinder to run way rich at idle only, and since you have feedback control of idle mixture, the computer will happily run the rest of them lean. Problem goes away off idle since fuel delivery off idle is pretty much normal. Check the plugs for signs one cylinder is running rich all (black or dark brown insulator tip).

Peter