Originally Posted by Carlo(s)

420SE V8 1986, 125K miles; Car was operating in top shape with smooth idle no cold/hot start problems, excellent power, just as a MB in top shape does. Out of nowhere after a short 5 mile run to the store, it started idling rough and idle surging just out of nowhere. Has had recent timing chain/rails, plug wires/cap/rotor 1 yr. old, plugs are all OK and just cleaned. Did electrical check plenty of juice to all plugs; fuel pumps working; changed OVP relay; did fuel check loosening injector lines all showed plenty of gas coming in; checked distributor all OK; no vacuum leaks anywhere. Fuel filter has less than 5K miles. Tapped idle selenoid in the engine and idle relay under passenger floorboard with no change. I'm puzzled because this situation arose immediately after I started the car at the store parking lot. Car still has plenty of power although it seems to have a slight misfire. Placing hands in the tailpipe discloses smooth idle then surge with a ppppt, ppppt, (uneven exhaust flow). I am puzzled and would appreciate some help.