The 6 liter motor in my truck surges between 450 and 600 RPM at idle. The computer shows no codes could this be a mass air sensor or a tps or does it need a tune up? It has 83000 miles.
I will bet that since it is a 6L with 83K that it needs a top end cleaner and followed by a new set of plugs. Most of the top end cleaners are easy to use because they have hoses to plug into.