420sl fast idle

im having some difficulties with a 107 420sl . sometimes it will not idle below 2000 rpm,and curiously the abs warning light then lights when this problem occurs- clearly there is some sort of electrical problem but where do you begin to look?!. do the abs and one of the fuel injection components share a relay or an earth somewhere? help greatly appreciated.

I think it's called the over voltage protection relay. it's an easy fix.