1988 560SEC, engine runs fine and performance is strong... but at cold start the idle hunts while warming up. Again, after the engine is warm and the transmission gear is in the park position, the engine idle jumps up and down (oil pressure gauge jumps simoultaneously).

My vehicle was recently tuned up and passed its smog inspection with flying colors (plugs, wires, cap & rotor, O2 sensor). No fault codes stored.

At 145k miles, I suspect a failed over voltage protection relay, idle control valve, but I'm not sure if I am on the right track. Just a hunch!

Please help!!

If its the same setup as the 300 then yes I change both also check hoses t idle vale for leaks

Thanks for your help... I will give that a try!