Idle Variation When Letting Off Gas

[rrb6699]

decided to make a seperate post for this.

my 96 2wd 5.2l

when I drive everything is fine. my idle is steady and no check engine codes.

however, very specifically, when I let off the gas over 45mph, the truck idle will drop 200rpm or so, then rise back up. it will do this until my road speed is under 45mph then it stays steady. if I let off the gas below 45mph it doesn't do this. if the truck is cold it doesn't do this until about 5mi of driving.

could this be the transmission? I'm thinking maybe the shift solenoid. I can feel resistance coasting above 45mph as if it were trying to downshift then stops.

if I keep a little gas it also doesn't do it.

any ideas?

 

[rrb6699]

update. when I take the truck out of overdrive the idle Variation happens at lower speed. but not with o/d engaged. I think shift solenoid or sensor? is speed sensor the only one for transmission?

I'm eliminating idle or tps since the throttle is in the same position when coasting under 45mph or stopped.