Why is my TPS reading WOT when throttle is closed?
 

After a MASS AIR conversion and Supercharger install. My car runs like S$#T I kinda traced the problem to the TPS, it is reading 4.92 volts with the car not running and the throttle blade closed. A buddy of mine said the TPS was working in reverse could this happen? Is there a difference in TPS Sensors between the 86-88 and the 89-93 mustangs. The computer and wiring harness is from a 90 and the computer is a 9AL. Can anyone help.

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Michael "Deke" Gramsch
87'GT - Oxford White (soon to be vermillion red)
Powerdyne 9 PSI Supercharger, 30# fuel injectors, Pro-M 77mm
MSD 6AL ignition and coil, 65mm FMS throttle body, K&N filter, Accel Pro Billet Distributor, Fluidyne Radiator and Blue Hose Kit, Long Tube Headers, Off Road H-Pipe, Flowmaster American Thunder Exhaust, MAC Shifter, Weld Draglites, 190 LPH Fuel Pump, ADJ Fuel Pressure Regulator & Fuel Pressure Gauge, and some other odds & ends.

TPS should be the same, but this would cross into the speed density v. Mass air arrangement of components that complimented to different air measurement systems. Best bet would be acquiring a new TPS from a MASS AIR car and replacing and checking. I have little experience in speed density and the supporting systems. Maybe you need to swap to see.

Pull it off the throttle body and rotate the blade so that it's reading .98 volts and then remount it on the throttle body.

Is it possible to mount it backwards? The wires coming off TPS should point toward the back of the car.

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351W 89 Mustang GT Convertible