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!!