99 F350 dually 2wd
V-10, 200,00 miles
Idle goes up & down, sometimes it will stall,
no codes, cannot find any vacuum leaks, going to replace PCV valve,
any ideas?

 

Also, check your IAC - Idle Air Control valve.

 

Sounds like a stuck IAC - the computer is trying to control the idle and can't.

 

I've had 2 IAC valves go bad, one on a V10 and another on a 4.6L. neither threw a code.

 

Thank The the help.
II picked up an IAC.
Can I take the throttle body off to make it easier to replace it?

 

You can, but there is a gasket between the throttle body and the intake that might need to be replaced.
The IAC has no input to the PCM so there would be no codes for it.
The throttle body butterfly plate completely closes at idle and the only way the engine gets any air is thru the IAC valve which is controlled by the PCM.

 

Thankx
I'm going after a gasket for the throttle body.

I'll let ya know how that goes.

 

Make sure to note how old IAC is installed. I got a cheap motor once because previous owner installed the IAC upside down.

Motor will not run right if IAC is installed upside down.

 

While you have the throttle body off inspect the throat below the butterfly for gunk.
Clean with carb cleaner if needed.
I remember a post where idle/running issues were caused by a layer of gunk down there.

 

Thankx.
Itz pretty dirty.