560 sel rough idle
 

I have 86 560 sel with 98000 miles. It develops a rough idle after about twenty minutes of driving.Let it set for a while start it up no problem drive it for a twenty or so minutes rough idle returns.Any suggestions would be greatly appreciated.

under the windshield washer mech (center, after the soundshield/firewall) is a black retangular box with a set of wires coming into it. Inside the box (which has a protective cover that can be pried off) is a circuit board. My rough idle was due to sliver crack in the solder- that as it heated up expanded and caused the solder to not allow the current and thus rough idle. You also have the idle control valve near the front of the engine- it's a grey/silver cylinder about 3 inches with a two wire prong and two air ports. Passenger side just in front of the air cleaner. That may be the culprit also. check plug wires, and plugs. Are you using 20-50 motor oil? you ought to.

Checked the board didn't see any cracked solder tracks.I think it might be the idle control valve.Tapped on it with screwdriver rough idle went away.Can this be cleaned or should I replace it. Thanks for your help

You can clean it with some brake cleaner fluid- may not help, may help for a bit or for some time. The things are expensive, but you can always go tot he junkyard and find one. If not drop me a private message and I'll be able to find one in a junkyard here in South Florida.

I just replaced the idle control valve on my 87 560SEL. Got rid of the rough idle, but now it is idling high. Idle control unit,(passenger side, under carpet, toe area, is my next culprit. You might check both. I got a brand new control valve for $226 when everyone else sells them for anywhere between $350 - $500.00. If you determine that is the part that you need, send me and e-mail at jardrewer@aol.com, and I'll put you in touch with my supplier. Good luck!!