Sure sounds like an OVP relay problem. The contacts sometimes mess up and and the voltage supply to the ABS and CIS-E becomes intermittent which causes the ABS light to come one and your idle smoothness to go south. I would rock the OVP a bit in its socket to see if that does anything. Pull it off the socket and inspect the contact pins. Also, make sure the fuse is ok and properly seated.

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W163 ML230 EURO SPEC 1999
W124 300E 1986