Mustang throttle position sensor

12/15/2009 small revisions in wording

The first thing everyone should understand is just because a meter says xx.xx volts, it does not mean it is absolutely that voltage. Most cheap meters I've looked at do NOT hold the implied specs. They are closer to 1/2% of actual scale, not the reading. So a meter on a 20 volt scale is generally within .1 volts of the reading, whatever it is. This is a price we pay for cheap imports. A good meter costs around $200 or more. It's like a torque wrench for voltage. We shouldn't expect perfection from a cheap $30 tool. 

Always measure throttle position sensor voltage by connecting your meter between the black and green leads. Never measure from the green lead to an engine component or bolt. This is because the computer reference is to the car chassis inside the passenger compartment, and the black throttle position sensor wire is referenced to that ground point.

Voltages you should see at the TPS (throttle position sensor) with ignition key on and engine off are:

Orange to black.....5.0 volts nominal

Green to black without TPS connected....anything from 0 to 5 volts. It is unpredictable because this is a computer input voltage, not output. It is very sensitive to leakage when the TPS is unplugged.

Black to vehicle chassis, timing chain cover, bell housing, or engine block....less than 0.5 volts under any operating condition

With the TPS connected idle position voltages should be....

Orange to black......5.0 volts NOMINAL depending on your meter

Green to black........0.6 volts to 1.1 volts, .9 or 1 volt is very good

Green to black with accelerator floored....at least 3 volts higher than the green to black idle voltage! The stock computer thinks WOT is 2.71 plus the idle voltage, WOT has to be about 3 volts more than idle voltage or the computer won't go into wide open throttle with the accelerator floored or nearly floored.

One additional important test:

As the accelerator is slowly moved there should be a smooth steady change on the green without any sudden jumps in voltage. This is best seen on an analog meter (one with a moving needle)! This is important for the acceleration enrichment to work, and for functions that depend on the relative throttle position.

It is important to test everything above. It is foolish to drill the holes out and set the TPS for exactly .xxx volts and call it done without checking the things that actually make a difference. The computer doesn't care and does not change anything regardless if idle voltage is anywhere between .6 volts and 1.1 volts. Any voltage within the idle range of .6 to 1.1 volts will be the same. Contrary to myths or rumors you do not need to have .97 volts to eliminate stalling, idle surge, or other problems!