Robertn421

I have a wonderful 99 E320 wagon with approx 85,000 miles. Recently it has had a high idle even after warming up. When I am at a stop in drive the idle is high enough (approx 800 rpm) to cause a shutter. I usually have to slide it into Neutral until I can move again? I have run a shop grade cleaner through with a tank of gas because a shop said these cars were known to do this if the intake valves were gunked up? It did not fix it. What should be my next thing to check or replace? Air Filter? Fuel Filters? Sensors? Thank you in advance for any help you can provide?