Hey everyone.
I see this is an old thread but have the same issue on a Yale 4.3 spectrum. Runs at extremely high idle and if you hit the gas it will set a code 638 and shut down. My sensors are sweeping good on volts.

I took the throttle body off to clean it out and still have the high rpm and fault. I hooked it up to the machine while I had the mixer off and the throttle was off the manifold. I thought, if I remember correctly, when you first key on the truck the throttle will open and close via the stepper motor. The motor is making a high pitched noise but no movement. Seems like it is only working via the accel cable side. I'm assuming my gears are stripped as well. Anyone have the same issue with similar symptoms?

Thanks!

k i will try this tomorrow but no lights are on will re post tomorrow

Do you have any codes is the MIL light on. It is possible you have a problem with the elctronic govenor assembly.

This symptom is associated with a code 638.

What happens is the gears in the trottle assembly get stripped out. The TPS and the FPP end up 20% or greater difference in voltage and the ECU shuts the engine down

You can blink the codes out by jumping A-D you will see each code 3 times and the codes are 3 didgets not 2. The connector is located down by the ECU

model number is h50xm sir number is h177b51815b thanks in advance

checked all fluids ok disconected oil preasure switch still stalls i will try the fuel knock off to day and also get the model and sir number

Check your motor oil level?
Really, having the correct model and serial number series is "a must have" to be able to give you more correct information, but it would seem to me what is most likely happening is that the fuel lock-off is getting power during the 'cranking' phase, when the key switch is in start and starter engaged, but then runs out of that fuel when the key is moved to the 'run' position. You should be able to test that with a test light or meter at the lock-off. some units have an optional oil pressure shutdown system that will do this if you don't have motor oil. [among a lot of other possibilities]