TP sensor graph of signal voltage vs throttle shaft rotation wit…

Throttle Position Sensor/Signal Response Graph
IF THE IMAGE IS TOO SMALL, click it.

This voltage is measured with the TPS connected normally, the key in RUN, the black meter probe on the SIG RTN wire (Bk/Wh or Gy/R), the VREF wire (Br/Wh) at 5VDC, & the red probe on the TP wire (DG/LG or Gy/Wh). Use pierce probes through the wires (or stickpins), or back probes in the connector.



The response signal must remain within the bright green area through the throttle's entire travel to pass. The dark green trace is good; the rust brown trace is a fail because it runs outside; the pink trace is a fail because it begins outside.

See this diagram for applications:

4.9L ('90-95) MotorCraft CX1426
V8s ('87-95) Motorcraft CX1228

Only very old TPSs require or allow adjustment. Modern EECs adapt automatically to the TPS output at startup, as described below. BEFORE attempting to adjust the TPS idle voltage, confirm that the throttle stop screw has not been tampered with. For the full procedure to reset the throttle stop screw, see this caption:


Idle Speed Control Closed Throttle Determination

One of the fundamental criteria for entering rpm control is an indication of closed throttle. Throttle mode is always calculated to the lowest learned throttle position (TP) voltage seen since engine start. This lowest learned value is called "ratch," since the software acts like a one-way ratchet. The ratch value (voltage) is displayed as the TPREL PID. The ratch value is relearned after every engine start. Ratch will learn the lowest, steady TP voltage seen after the engine starts. In some cases, ratch can learn higher values of TP. The time to learn the higher values is significantly longer than the time to learn the lower values. The brakes must also be applied to learn the higher values.

All PCM functions are done using this ratch voltage, including idle speed control. The PCM goes into closed throttle mode when the TP voltage is at the ratch (TPREL PID) value. Increase in TP voltage, normally less than 0.05 volts, will put the PCM in part throttle mode. Throttle mode can be viewed by looking at the TP MODE PID. With the throttle closed, the PID must read C/T (closed throttle). Slightly corrupt values of ratch can prevent the PCM from entering closed throttle mode. An incorrect part throttle indication at idle will prevent entry into closed throttle rpm control, and could result in a high idle. Ratch can be corrupted by a throttle position sensor or circuit that "drops out" or is noisy, or by loose/worn throttle plates that close tight during a decel and spring back at a normal engine vacuum.

BEFORE attempting to remove the TPS, see this caption:


For other sensors:


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Part of 1980-1986 Ford Bronco Manual Pages

Owner caption May 2020 · Photo 5777 of 6546