Idle too High??
 

I have had a running problem with my 1998 C280. It seems to have an idling problem, but only in Drive not reverse or neutral. The car shakes as if it was idling poorly but it really is just idling too fast. I have runs the codes and only got P0400. I have cleaned the EGR tube and EGR itself and replaced the MAS. No help. Today the problem went away, It was much warmer today 75 degrees. The car didn't shake at idle and the idle seemed a littler lower. Has anymore had this problem? Does anyone know how to fix it. Love the car but it idles like a 1973 pinto (sometimes).

Thanks

Abox5