Possible bad TPS sensor. With ignition OFF, disconnect the sensor, put an analog ohm meter to the center pin and one of the edge pins. Operate the throttle. Depending upon what side of the sensor, you'll read high ohms that will drop to almost zero or almost zero ohms that will rise. The direction doesn't matter, the ohm meter needle movement should be smooth with no sudden jumps. If I'm right, there will be an drop towards the high side of the resistance.
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Good Luck...
mj
'01 Ford Ranger 3.0 Super Cab, K&N Air, MaxFlow Exhaust, Oversize Tires 
'93 Ford Taurus 3.0 (Ugh! What a MONEY PIT! Traded it in for the '01 Ranger) 
'87 Ford Ranger 2.3 Super Cab (Owned it for 16 years until some clown t-boned me in it!) 
'92 Ford Aerostar 3.0 (Gave it to Ex in Divorce Settlement) Hehe...
'74 Ford Maverick 250 ci (Great car! 110 mph on Autoban! Traded it in for the '87 Ranger)
'66 Ford Mustang 200 ci (Screwed up and SOLD IT!!)  | 
