I've noticed after prolonged highway driving (100+ miles), the idle dances between 550-800 RPM. It's mainly noticeable when pulling off the highway and stopping for gas or something. The car runs fine but it's just strange. Never happens when driving around town or local highway driving. Air filter's clean, only use Top Tier 91+ gas, synthetic oil, clean tranny fluid, coolant level good and fresh, clean MAF each year. I'd think a vacuum leak would manifest itself all the time, not just after prolonged driving like this. Sounds like some sensor is getting hot and acting wonky. Any ideas?

 

Bumpity Bizzump