Another 560 sel rough idle
 

I have posted before but I have some more info.It is driving me nuts.Car idles rough, warm or cold.Idles at about 600rpm.It is not missing just rough. When I accelaerate from a stop it is as smooth as silk. If I put in neutral and rev engine to 1500rpm once again it is so smooth it is unbelievable. Accelerates great and runs smooth under load or at 1500 in neutral.Has a starting problem.Start it and immediately dies.But always starts on second attempt.If it sits for a while it usually starts right up but still idles rough.Any ideas.Love the car once you are going you cant even tell the engine is running!

Its about time for a fuel distributor and or EHA.

anybody else?

Look for vacuum leaks, if it has a EGR valve, it may be stuck open. That would be were I would start based on your description of symptoms. Vacuum leaks would likely be a easy and reletively cheap fix if you find any.

checked the EGR seems to be working

also unplugged EHA with no effect on the idle

Anything else guys

Intake Manifold
 

My 89 420SEL had a rough idle. Replacing the intake manifold O rings made a world of difference. I'm no mechanic. Have you replaced the O rings? If not, they will be rock hard from the heat, and may even be split.

I'd replace the spark plugs with new Bosch Coppers and go from there...it really worked for me. best of luck

If you really want to go crazy throw a new coolant temputure sensor on as well...figure $30 for the plugs and $50 for the sensor...less than $100 out the door. That's where I would start on this one....regards

I had a rough idle on my '89 300E and after replacing plugs/injectors/filters/etc it turned out to be the ignition wires. I have a '91 560SEL with the exact same idle problem, replaced all the rubber, fuel pressure regulator, idle control valve, got a rebuilt fuel distributor with new EHA valve and still runs rough. Got new wires and going to install them this weekend, will let you know how it turns out.

While it's idling rough, squirt some carb cleaner into the intake. IF it suddenly smooths out then your FD or injectors may be blocked or it's running too lean.

If not, pull the plugs and check the condition and if they are gapped correectly and also check the condition of the cap and rotor.