Idle problem only in park! on 1996 Mercedes-Benz SL600

I just purchased the car & it was extremely low on fuel.I filled it up with 93 octane/lucas engine treatment, & tokk it to a laser wash.It drives perfect on the highway,stoplights idling, but once you put it in park it will idle up to 1250-1300 rpm's then down to 600-650 all by itself at about 5 second intervals.Trash in fuel?MAF?

1 answer
Your car has on board diagnostics level two, a scantool may show irregularities with live sensor data without having to intrusive testing at each sensor or harness connection. I am not experienced in Mercedes but Honda and Toyotas that do this could be due to something as simple as the engine coolant level being low. On your car it could be the idle control system, sensors here are the, throttle position switch, idle air control actuator, air flow meter/MAP sensor and coolant temperature switch,