After driving my '82 300D Turbo for a while when you stop the car and put in park or neutral the idle rpm's begin to climb. This always happens when I park the car and put it in park before turning it off. I can get it to stop and idle properly by nudging the 'gas' pedal backwards with my foot. So I think the gas pedal is a tad sticky, but I can't see where to check for this and possilbly lube it. Any suggestions?