what would make rpms rise when truck starts to move in nutral with clutch out???

[woodturner50]

still having truble with rpms, now I found that if i stop on a slite slope and let the truck come down to a low idel 900, then take foot of brake and let the truck coast the rpm will start ot rise to about 2500 and let it coast till it comes to a stop only then will the rpms come down to 900.
I have no check engine lite on, I have used a propine torch (not lit) to check for Intake leaks. checked IAC and TPS, let the engine come up to temp, unpluged one at a time and bouth made the rpms go down to 500 so i think thay work. the heat guage come up to very low in temp, will not running at right temp make this happen?? and it stills stay at high idel when i am driving and shift gears.
Thanks again Ron

 

[briwayjones]

I'm not exactly following you. But if you're coasting in say first gear with the clutch out even though in theory the RPMs should go down to idle the ford computers keep the RPMs at about 1200RPM in my experience and won't go down to idle until you push in the clutch. If you're coasting down a hill with the clutch out than the engine is compression braking which will make the RPMs go up because the inertia of the vehicle is making the engine turn faster by actually driving the engine. Did that answer your question?

Are you saying that if you coast with the clutch pushed in or in neutral that the RPMs go up to 2500?

 

[rwenzing]

There is an EFI emission feature called dashpot (after the old carburetor dashpots) that uses the IAC to hold the RPM above the base idle during deceleration or while shifting gears. This reduces hydrocarbon spiking caused by a sudden vacuum change.

I would check to see if the TPS is returning >1.53v to the PCM with the throttle closed. If so, that is your problem which could be caused either by the throttle hanging slightly open or by a bad TPS.