My (new to me) 1990 F150 5.0 AOD, has recently developed an odd one. It will idle slightly rough, the tach needle will fluctuate slightly... if you accelerate.. the engine will speed up, still missing some, but the needle will start to swing back and forth FAR above the actual RPM, and then far BELOW it, say about 500+ and then -rpm swings... if you keep pressing for power, it will buck a bit above say 2500 rpm.... Today in town, i made a few stops, when I came out, and started it up again, it ran Smooth.. tach tracked NORMALLY....and accelerated perfectly!
Once back home... went back out.. and it's back to acting up. Has new gas filter, cap and rotor, Good ( less than 5000 miles) wires and plugs. Air filter is ok. Throttle Body cleaned. Sea Foam in the gas tank.

Where do i start looking??

 

Throttle Position Sensor sounds like

Duralast/Throttle Position Sensor (TPS228) | 1990 Ford F150 1/2 ton P/U 2WD 8 Cylinders N 5.0L FI | AutoZone.com

Check for codes....

 

The TPS can made it act like that???? Had one go bad in a Ranger before. but it had different symptoms... But I'll test it tomorrow.

 

Pull the codes before you start guessing at possible causes, in my experience this type of miss is ignition related and that should generate a code for the PIP or IDM signal and if so you need to replace the module inside the distributor(PIP) or the TFI module on the outside of it.

 

It was the TFI module. Popped the dizzy out, took module to be tested.
Passed first time, but once WARM... FAILED! Also replaced Coolant Temp Sensor, since it was right there with Dizzy out of the way, and It was Hot starting hard too.
BOTH problems solved.. runs like a Singer sewing Machine now! Idle's smooth as silk. Thanks Guys!