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Some manufacturers state an ideal range for throttle position sensor which is helpful if you want to calibrate a new sensor or re-calibrate the old one. For instance, they say 0.5 V for idle and 4.5 V for full throttle (WOT). I didn't find any voltage numbers for my car in the manual. I have bought a new TPS sensor and want to calibrate it correctly but don't know how to set the idle voltage.

Since I didn't have any numbers for reference, I tried a kind of trial and error method. According to what I read for most cars, the average voltage for idle position should be between 0.4 V and 0.6 V. Therefore, I started with 0.4 V, then increased it to 0.43, 0.44, 0.45 and went on all the way up to 0.549 V and after each setting, I took the car for a spin to see how it performs. However, I'm still not quite sure which setting is the best.

What happens if full throttle voltage is slightly lower than 4.5 V (say 4.47 V)? Does the ECU still recognize it as WOT? If not, does it reduce engine performance?

Why is the voltage not the same when the engine is off and on? I saw about 0.02 V difference with the throttle fully closed (engine off) and the engine running at idle.

Can an incorrectly adjusted TPS cause engine vibration at idle?

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  • Why are you replacing the TPS? Are you sure it is faulty? Do you have any error codes?
    – HandyHowie
    Feb 7 at 7:49
  • If your manufacturer doesn't specify it may be that it self-calibrates by taking the max and min voltages from the pedal position. Are you sure you are supposed to do this manually?
    – GdD
    Feb 7 at 13:39
  • Why are you replacing the TPS? Are you sure it is faulty? Do you have any error codes?
    – HandyHowie
    Feb 9 at 15:44
  • @HandyHowie - I replaced the TPS not because it was faulty. I didn't have any error codes either. I replaced it because it was the original TPS after 12 years in service. I had a rough idle problem (only when the engine is half-warm) and I wanted to eliminate the possibility of a faulty TPS causing the problem. Feb 9 at 16:13
  • @GdD - No, I'm not sure but I have seen many instructional videos on Youtube on how to calibrate your TPS the best way using an ohm meter and things like that. Feb 9 at 16:16

2 Answers 2

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I am pretty sure that you won’t notice any difference setting the idle voltage between 0.4v and 0.6v. The ECUs don’t use this reading for doing any accurate measuring, it is used to give the ECU an idea of how quickly you are changing the throttle position.

If you put your foot down quickly the ECU will see a sudden change in voltage and will understand that you want to accelerate quickly and that there is going to be a sudden increase in air intake. The voltages are not really that important just the rate of change.

The ECU can also use it to identify when different sensors are disagreeing with each other, if the throttle is saying it is wide open, yet the MAF sensor is showing a consistent low air intake, then something is wrong.

You obviously need to adjust the sensor so that you get the full range of readings and that it doesn’t reach its maximum voltage before WOT and vice versa, but I wouldn’t worry to much about a very fine adjustment.

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  • Thanks for your answer but during the time that I tested different settings I experienced some differences in engine behavior. When I set the idle at 0.48V, it was jerky when I let off the throttle. I changed the setting and it got smoother. When I set it at 0.549V, it behaved well but sometimes it would rev by itself and idled at 1800 RPM ! This is why I wanted to know which setting is the best. Feb 6 at 14:30
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    @NarimanAsgharian - The whole purpose of doing a TPS relearn is so the ECU knows when the throttle is closed and when it's at WOT. It does this by reading what voltage is at the given positions. Because of this, it really doesn't matter what the voltages are. If the TPS relearn is done correctly and the mechanical parts in question are in good repair, the ECU will know what the values should be and will respond accordingly. Feb 7 at 12:22
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    @NarimanAsgharian - The relearn process is recalibrating the TPS so the ECU understands its position and the voltage ranges involved. Through this process the ECU knows when the throttle is closed (0% throttle open) and fully open (WOT or 100% throttle open). Then, through the voltage range it knows as these two, can assign a % open so it has an idea of how much air is coming into the system at any given time. Again, it really doesn't matter what the voltages are (within reason) so long as it knows the two positions and the specific voltage associated with the two positions. Feb 7 at 21:27
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    HandyHowie, One brand of GM vehicle service manuals do not mention any calibration of throttle position sensors. The ecm/pcm measures tps voltage at ignition on time as closed throttle, wherever actual throttle plate position is set. In one GM model, worn tps' inadvertently raised idle rpm consistently. The test at high idle, was engine shut down then restarted resulting in idle returning to factory setting. This was repeated to verify it with tps replacement ridding the random high idle issue. I don't know if every EFI system reads tps value at ignition on time.
    – F Dryer
    Feb 8 at 17:58
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    Nariman Asgharian, User manual - is this the owner's manual? Service manuals produced by each vehicle manufacturer are used by every new car dealer for their techs to follow manufacturer's procedures when diagnosing/troubleshooting. The public can buy these manuals, subscribe to Alldata.diy or Mitchell for online access to manufacturers service manuals. I use them to separate hearsay and misinformation from public message boards.
    – F Dryer
    Feb 8 at 18:05
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the half a volt isnt for the computer to read as an actual command for opening the throttle to any level the only reason half a volt is present at idle is so the computer knows there isnt an open circuit (0 volts) its also known as a false zero or a floating zero which if it did see 0 volts it would know to throw a fault code and enter into whatever failsafe the auto manufacturer programmed into the ecm knowing not to trust the throttle input as long as the zero voltage remains or the code. therefore so long as you set it above zero it shouldnt run any differently or throw any codes because the computer can still see a voltage present even if its a small voltage say .2 or .3v

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  • Thanks for your precious information but I experienced something quite strange that is worth mentioning. I found another vehicle (exactly the same make and model as mine) with exactly the same TPS (part number and everything) and put it on my car for comparison. I set it at exactly the same voltage as my previous TPS. So, everything was exactly the same! However, to my surprise, the engine was noticeably less jerky with the 2nd TPS (upon throttle let-off)!! I don't have any explanation for this phenomenon! Feb 9 at 14:58
  • ive had that same expeerience before with mass air flow sensors And im pretty sure when it comes to sensors that have higher resolution and are constantly changing like that even minute voltage annomalies a bad sensor might give off would confuse the computer and these annomalies may not be visible with static voltmeter measurements we would be taking so unless you connect an osciliscope and monitor the waveform during operation its unlikely that you would be able to see what the issue that is throwing off the computer is Feb 13 at 22:05

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