91 r129 500sl rough idle issues
 

Hi I am new to this forum as I have just purchesed my first mercedes and I am having some issues with the car at start up and at idle. the car takes a moment on cold start but starts fine once warmed up but the idle is rough and remains rough at all times.can any one give me some direction I have replaced the.
plugs
wires
caps
and rotor buttons.
thought about idle air control valve but dont want to throw parts at it as we know they are not cheap Thanks Bill

I would start by checking for vacuum leaks.

For sure. Check all the vacuum hoses, and also, the rubber air intake plenum between the air meter and the manifold, and the injector cup seals. Those are all places known to be likely causes of a vacuum leak. If you rule out vacuum leaks, you might have a dribbling injector or two.

Have you done a compression test on the motor yet? Are all eight cylinders in spec?