Throttle Position Sensor (TPS)

 

     The throttle position sensor is mounted on the end of the throttle body and tells the computer how far open or closed the throttle is.  The TPS is pretty easy to understand how it work’s, it is a potentiometer just like your dimmer switch in the dash.  Voltage is fed to the TPS by the signal return circuit.  As the throttle is opened the TPS directs more voltage to the EEC and less down the voltage reference circuit.  All of the following items will affect the TPS:

     The TPS sensor has a great deal of influence on the fuel ratios and timing curves, because the TPS is a user interface sensor.  The TPS is the closest thing you have to a phone call into EEC.  EEC listens to your every command by the throttle.  The TPS is fourth in command in the hierarchy of EFI sensors, which means your decisions are pretty important to EEC and its decisions.

     Before testing the TPS or any other EFI component perform a self-test, trouble codes received during test can be used as a diagnostic tool along with other indicators.  To test the TPS sensor you will need a volt meter.  You need to back probe the harness while reading the voltage between the TPS and SIG RTN pins.  The exact voltage you get at any one point is not of major concern; instead you need to watch for a smooth increase in voltage as the throttle is moved.  A TPS that does not give a steady increase in voltage as the throttle is moved is faulty and needs to be replaced.

Throttle Position Sensor

Rotational Angle

Signal Voltage

0

Under travel

0.000

10

0.450

13

Closed throttle

0.901

20

 

1.440

30

1.900

40

2.370

50

2.840

60

3.310

70

3.780

80

4.240

84

Full throttle

4.538

90

Over travel

4.780

100

5.000

Values were calculated for VREF=5.0 volts.  These values may vary 3 percent due to sensor and VREF variations

 

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The three wires going to the TPS are:
+5V reference = from the PCM
signal output = 0.95-4.95v or so to the PCM
ground = 0 volt reference
So when measuring from ground or the engine block to the signal output wire you should read about 0.85 to 0.98v in idle position then close to 5V at WOT. This should be checked with the key on but engine off. Also check that the voltage changes smoothly from idle to WOT. If it suddenly jumps around then the wiper or resistor element is bad.
When you installed the sensor make sure you place it on the peg right and then tighten it down properly. Loosen the back screw a tiny bit so the sensor can pivot and loosen the front screw enough so you can move it just a little in very small increments. I wouldn’t try to adjust it using marks. Set it at .97v-.99v, the closer to .99v the better. Just don’t go over .99, or you upset the fuel calibration and idle quality will suffer.
(copied from MustangMax, Glendale AZ)
1. Always adjust the TPS and Idle with the engine at operating temp. Dive it around for a bit if you can and get it nice and warm.
2. When you probe the leads of the TPS, do not use an engine ground, put the ground probe into the lead of the TPS. You should be connecting both meter probes to the TPS and not one to the TPS and the other to ground.
3. Always reset the computer whenever you adjust the TPS or clean/change any sensors. I just pull the battery lead for 10 minutes.
4. Check the procedure for your year, on my 90 I have to turn the idle screw until it just touches the tab, then insert a .010 feeler gauge and give it about one more turn. Then you adjust the TPS voltage to .98v, reset the computer. Start it up, if the idle is to low then turn the screw in until it is just right, then readjust the TPS voltage to .98v and reset the computer and start it up. The key is to adjust the TPS voltage and reset the computer whenever the idle screw is changed.

"Wiring conversion for the explorer TPS
99 Explorer TPS
BRN/WHT - is for VOLT REF.
GRY/WHT - is for TP SENSOR INPUT
GRY/RED - is for SIG RETURN

89 Mustang TPS
ORG/WHT - is for VOLT REF.
DRK GRN/LT GREEN - is for TP SENSOR INPUT
BLK/WHT - is for SIG RETURN"