TPS, Throttle Position Sensor, is a 5volt sensor
It has 3 wires, 5volt, return, ground
Key on engine off
Usually upper wire is 5v and lower is the ground
Center is the return
You can use a sewing needle to pierce any wire to test voltages, won't hurt the wire, push needle in at an angle so it contacts the "wire" inside insulation
Throttle closed spec is 0.69 to 0.99volt on center wire
WOT is 4.5volts to 4.7volts, never 5volts
In % this is 17-19% throttle closed, and 90-92% WOT
1volt is 20% of 5volts, just under 1v is throttle closed
4.5volt is 90% of 5volts, 4.5v or higher is WOT
You never want a 5 volt sensor's return voltage to be 0volts or 5volts otherwise its no good as a sensor as its range compromised, it must be higher than 0v and lower than 5v
TPS has 4 uses
Main use is to give the computer a "heads up" when gas pedal is pressed down, MAP or MAF sensors are slow to respond to changes in air flow, i.e. throttle opening
So without the "heads up" the engine would stumbled on acceleration until computer added more fuel based on MAP or MAF changes
Carburetors had an Accelerator Pump to squirt in the extra fuel when gas pedal was pressed down, fuel injection has the TPS
Foot off the gas pedal(TPS under 1v), with engine RPMs above 1,500, coasting, computer will shut off fuel injectors for coasting, this is one of the MPG benefits of fuel injection
TPS under 1volt, computer ignores O2 sensor(s), idle needs to be a richer mix to prevent overheating
TPS at 4.5v, computer ignores O2 sensor(s), it runs max. fuel for the RPM/load for best power, foot to the floor means "driver is not concerned with MPG" at that time, lol
Engine load, computer uses RPM, MAP/MAF data and TPS voltage to calculate engine's load so it can then calculate best air/fuel mix and spark timing
Its possible TPS could cause a rough idle but wouldn't be first on the list
Smaller vacuum leak would be more common, vacuum is highest at idle and O2 sensor is not being used, so a smaller vacuum leak could foul up the idle mix, lean mix
Same for fuel leak, Fuel Pressure Regulator(FPR) could have a small leak into the FPRs vacuum hose, or a leaking injector tip, so with O2 sensor off line its a richer mix, MPG would be effected overall
When you step on the gas pedal O2 sensor comes back on line and computer is now controlling the mix on the fly
If your MPG is not what it should be then change the O2 sensor first, only sensor that wears out, 12 years or 100k miles and they start to run out of the chemicals that detect oxygen, so MPG starts to go down and down and down, also can foul up idle because computer uses average O2 sensor readings when driving, called Long term fuel trims, to set the richer idle air/fuel mix
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