2000 Express 2500 intermittant fast idle...

My 2000 Express 2500 passenger van 8600GVW 5.7 is intermittantly fast idling. It will do this for a couple of days, or even sometimes only a few start/stop engine cycles, then mysteriously straighten outself out, only to start fast idling by itself at any time again. No evident vacuum leaks...Cold or hot engine--doesn't matter. Truck starts and runs fine, and has been doing this off and on for the past few months now. I wish it were not intermittant----would be easier to diagnose and fix. Starting to become frustrating...Except for this fast idle/high engine speed problem, this truck looks and runs great, has been well maintained, recent fuel pump, new PCM in past year. High mileage--235k. Any help or ideas appreciated....thanks. WJL

My 2000 Express 2500 passenger van 8600GVW 5.7 is intermittantly fast idling. It will do this for a couple of days, or even sometimes only a few start/stop engine cycles, then mysteriously straighten outself out, only to start fast idling by itself at any time again. No evident vacuum leaks...Cold or hot engine--doesn't matter. Truck starts and runs fine, and has been doing this off and on for the past few months now. I wish it were not intermittant----would be easier to diagnose and fix. Starting to become frustrating...Except for this fast idle/high engine speed problem, this truck looks and runs great, has been well maintained, recent fuel pump, new PCM in past year. High mileage--235k. Any help or ideas appreciated....thanks. WJL

Check computer for codes past and history and present and sensor readings and IAC valve control and EGR valve control.
Make sure PCV valve is good and hoses to it and all other vacuum lines.

Make sure IAC valve and throttle body butter fly clean.
When was the last good tune up?
Good Ac delco stuff?
Any codes or check engine lights or misfires?

Check computer for codes past and history and present and sensor readings and IAC valve control and EGR valve control.
Make sure PCV valve is good and hoses to it and all other vacuum lines.

Make sure IAC valve and throttle body butter fly clean.
When was the last good tune up?
Good Ac delco stuff?
Any codes or check engine lights or misfires?
Thanks MT......No codes, check lights, or misfires. Recent (17k miles ago)Delco cap and rotor. I have new AC plugs and Delco wires on hand, but haven't installed them as yet...I'll check PCV, EGR, and get IAC and TB butterfly clean when I pull cowl cover early next week....Would/could a bad TPS sensor make for a fast idling engine on this truck? Thanks. WJL

Thanks MT......No codes, check lights, or misfires. Recent (17k miles ago)Delco cap and rotor. I have new AC plugs and Delco wires on hand, but haven't installed them as yet...I'll check PCV, EGR, and get IAC and TB butterfly clean when I pull cowl cover early next week....Would/could a bad TPS sensor make for a fast idling engine on this truck? Thanks. WJL

Yes a bad TPS can but other sensors can to.
Let us know how it goes.