Engine/Transmission (1998.5 - 2002) Engine idle RPM changes

[jkern]

Ok, my truck has been doing this for a while now. While sitting stopped the tach indicates that the engine idles at slightly less than 875rpm (which in my opinion is plenty high). however once the speedometer get above 10mph while coasting dowhill in traffic or down the driveway in neutral, etc. the idle increases to about 950 to 1000rpm. once i slow back down below 10mph it drops back to around 875. any thoughts?

 

[SSolderitch]

I idle at 850. coasting - clutch in or out? I can pump enought air - no fuel coasting down a hill to cool the egt's to below idle temp of 225 degrees. Sounds normal to me.

 

[hcole]

This is normal. It tells you in the service manual that it idles at 950 rpm at any speed ABOVE 12 MPH if I recall correctly.

It idles at 875 RPM at 0 MPH. It gets its signal from the ECM I think where the wheel speed (speedometer) is also.