I've had an issue with CEL with code p0507 reading "idle system RPM higher than expected" intermittently come on every 70 or so miles with no other CELs coming on. It is very vague as to what could be wrong to cause a high idle consistent 1000-1200. I've cleaned and then eventually replaced the IAC valve along with cleaning my EGR valve and replaced my PCV valve. Inspected all vacuum lines and found one broke in half going to my EVAC control valve. Still it posts. Came down to using seafoam to try and clean my intake which made it idle VERY high afterwards up at 2000 then slowly work down to even out at 1500... There was a point it seemed to be fixed idling at 800-900 right after I changed my IAC valve but only lasted for 300 miles on the highway before that god damn CEL came back... I've currently taken off my intake manifold to check all the gaskets and for cracks in the IM itself. Gaskets good and no cracks... Any ideas or something I missed would help.