My 97 diamante after its at operating temp, the idle is hard with minor vibration and noise. It does not do it all the time. It is the worst after being on the highway and pulling up to a stop sign. I had the dealer clean the intake system for $100.00 and it took care of it for a while until I used some gas line antifreeze, then it came back.I had also cleaned the egr. No check engine light. The car has !88,000 miles on it.