Mustang TPS Adjustment - 0.999999v not necessary

Mustang5L5 · Oct 17, 2010

EDIT: This post applies to 86-93 5.0 Mustangs.

Seems to be a common myth, so lets sticky a thread explaining how the TPS works. Jrichker has provided the basic TPS guideline to follow. But here's a snip of the A9L GUFB which is the programming logic.

Pay attention to the part highlighted in yellow. More snips in post #42

So with that said, adjusting your TPS to .99999999 volts is not necessary at all. The ECU has a logic to account for variations due to production. Ford does not adjust the TPS at all when it is placed on the car. There is a general range the computer will accept as idle voltage for the TPS. This range is 0.5 - 1.25 volts. ANYTHING within this range is acceptable.

If idle voltage is outside this range, a TPS code is generated by the computer.

Code 63: Throttle Position Sensor signal too low (under 0.5v)
Code 53: Throttle Position sensor signal too high (over 1.2V)
Code 23: Throttle sensor out of range (with engine off)

Therefore, the only adjustment really necessary is to verify the tps voltage at idle is anywhere between the above range. If this is a FORD OEM tps, it should be. Aftermarket TPS's might be different and require you to slot the holes to get it in range. If it is in range, then you are fine. No need to chase the mythical 0.99 volts that has been tossed around for years. Upon vehicle startup, the computer will take the base idle voltage, and apply a certain voltage value to that number as the trigger point for WOT operations. I've seen 2.71-3.13 throw around as the value increase over baseline idle voltage as triggering WOT. The value is adjustable and can be changed by tuning

To make a long story short. If your idle TPS voltage is anywhere between 0.5V and 1.25V...you are good to go.

jrichker said:
TPS setting and troubleshooting

Revised 06-Oct-2010 to add open computer signal ground information.

Setting the TPS:
You'll need a good Digital Voltmeter (DVM) to do the job. Set the TPS voltage at .5- 1.1 range. Because of the variables involved with the tolerances of both computer and DVM, I would shoot for somewhere between .6 and 1.0 volts. Unless you have a Fluke or other high grade DVM, the second digit past the decimal point on cheap DVM’s is probably fantasy.

Since the computer zeros out the TPS voltage every time it powers up, playing with the settings isn't an effective aid to performance or drivability. The main purpose of checking the TPS is to make sure it isn't way out of range and causing problems.

Wire colors & functions:
Orange/white = 5 volt VREF from the computer
Dark Green/lt green = TPS output to computer
Black/white = Signal ground from computer

The Orange/White wire is the VREF 5 volts from the computer. You use the Dark Green/Lt green wire (TPS signal) and the Black/White wire (TPS ground) to set the TPS. Use a pair of safety pins to probe the TPS connector from the rear of the connector. You may find it a little difficult to make a good connection, but keep trying. Put the safety pins in the Dark Green/Lt green wire and Black/White wire. Make sure the ignition switch is in the Run position but the engine isn't running.

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.

A.) 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.

B.) 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.

C.) Always reset the computer whenever you adjust the TPS or clean/change any sensors. I just pull the battery lead for 10 minutes.

D.) The key is to check the TPS voltage whenever the idle screw is changed.

TPS testing:
Most of the time a failed TPS will set code 23 or 63, but not always. Use either an analog meter or a DVM with an analog bar graph and connect the leads as instructed above. Turn the ignition switch to the Run position, but do not start the engine. Note the voltage with the throttle closed. Slowly open the throttle and watch the voltage increase smoothly, slowly close the throttle and watch the voltage decrease smoothly. If the voltage jumps around and isn’t smooth, the TPS has some worn places in the resistor element. When the throttle is closed, make sure that the voltage is the same as what it was when you started. If it varies more than 10%, the TPS is suspect of being worn in the idle range of its travel. It should go from base voltage at idle to somewhere near 4.6-4.8 volts at WOT

TPS Troubleshooting:
The TPS sensor is a variable resistor like the volume control on most cheap radios. We have all heard them make scratchy noises as you turn them up or down. The resistor element can wear and cause a drop out spot in the output voltage. This confuses the computer because it expects to see a steady TPS voltage increase as the Throttle opens up.

TPS troubleshooting steps:
Some basic checks you can make to be sure that the sensor is getting power & ground:
Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.
Check the resistance between the black/white wire on the MAP/BARO sensor and then the black/white wire on the EGR and the same wire on the TPS. It should be less than 1 ohm. Next check the resistance between the black/white wire and the negative battery cable. It should be less than 1.5 ohm. More than 1.5 Ohm means you either have wiring problems or a open signal ground inside the computer. An open signal ground inside the computer will disable the TPS, EGR, ACT, ECT and MAP/Baro sensors. That will cause performance and drivability problems.

See Computer issue? - Mustang Forums at StangNet for more help on fixing the computer innards.

The following power on check requires you to turn the ignition switch to the Run position.
Use a DVM to check for 5 volts on the orange/white wire. If it is missing, look for +5 volts at the orange/white wire on the TPS or EGR sensors. Use the black/white wire for the ground for the DVM.

jrichker said:
Code 63 - Throttle Position Sensor (TPS) signal too low.

Revised 02-Jul-2009 to update TPS setting procedure & add 10 pin connector layout.

Vref missing (5 volt reference voltage supplied by the computer), bad connections or damaged wiring, TPS sensor failed, TPS sensor way out of adjustment. Use a DVM to check for 5 volts on the Orange wire. If it is missing, look for +5 volts at the Orange wire on the EGR or MAP/Baro sensor located on the firewall near the center of the car. If there is +5 volts on the MAP/Baro sensor, but not on the EGR, clean the #2 & #5 pin on the white 10 pin connector. If there is +5 volts on the EGR but not on the TPS, look for bad wiring inside the engine fuel injector harness.

Setting the TPS voltage
You'll need a Digital Voltmeter (DVM) to do the job.

Wire colors & functions:
Orange/white = 5 volt VREF from the computer
Dark Green/lt green = TPS output to computer
Black/white = Signal ground from computer

Always use the Dark Green/lt green & Black/white wires to set the TPS base voltage.

Do the test with the ignition switch in the Run position without the engine running.

Use the Orange/white & Black white wires to verify the TPS has the correct 5 volts source from the computer.
Setting the TPS: you'll need a good Digital Voltmeter (DVM) to do the job. Set the TPS voltage at .5- 1.1 range. Because of the variables involved with the tolerances of both computer and DVM, I would shoot for somewhere between .6 and 1.0 volts. Unless you have a Fluke or other high grade DVM, the second digit past the decimal point on cheap DVM’s is probably fantasy.

Since the computer zeros out the TPS voltage every time it powers up, playing with the settings isn't an effective aid to performance or drivability. The main purpose of checking the TPS is to make sure it isn't way out of range and causing problems.

The Orange/White wire is the VREF 5 volts from the computer. You use the Dark Green/Lt green wire (TPS signal) and the Black/White wire (TPS ground) to set the TPS. Use a pair of safety pins to probe the TPS connector from the rear of the connector. You may find it a little difficult to make a good connection, but keep trying. Put the safety pins in the Dark Green/Lt green wire and Black/White wire. Make sure the ignition switch is in the Run position but the engine isn't running.

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.

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.

The TPS is a variable resistor, must like the volume control knob on a cheap radio. We have all heard them crackle and pop when the volume is adjusted. The TPS sensor has the same problem: wear on the resistor element makes places that create electrical noise. This electrical noise confuses the computer, because it expects to see a smooth increase or decrease as the throttle is opened or closed.

TPS testing: most of the time a failed TPS will set code 23 or 63, but not always. Use either an analog meter or a DVM with an analog bar graph and connect the leads as instructed above. Turn the ignition switch to the Run position, but do not start the engine. Note the voltage with the throttle closed. Slowly open the throttle and watch the voltage increase smoothly, slowly close the throttle and watch the voltage decrease smoothly. If the voltage jumps around and isn’t smooth, the TPS has some worn places in the resistor element. When the throttle is closed, make sure that the voltage is the same as what it was when you started. If it varies more than 10%, the TPS is suspect of being worn in the idle range of its travel.

stang-geoff · Oct 21, 2010

Thank you for this post. Every ford publication has told me this and even my chilton, but everyone on the internet seems to say it's the mythical .99volts that you're suppose to have it set at. I was wondering if people knew something I didn't

NIKwoaC · Oct 22, 2010

Good post, Mike. People seem to think the TPS is some magical sensor that can make or break performance if you don't have it set exactly right (0.9999999999999999999V).

I'm adding this one to the "Really Common Questions" sticky over in Talk! Feel free to remove this post if you want to keep this sticky cleaned up, you won't hurt my feelings.

Mustang5L5 · Oct 24, 2010

Added more tech data. Hopefully any tps questions can be directed here

87mustang4001 · Nov 5, 2010

I adjusted my tps to the correct value now I'm getting code 85. Is this normal at 1.4v I get no code. Any lower I get code 85 please help.

jrichker · Nov 5, 2010

87mustang4001 said:
I adjusted my TPS to the correct value now I'm getting code 85. Is this normal at 1.V I get no code. Any lower I get code 85 please help.

Code 85 has nothing to do with the TPS. Any relation to code 85 and what you do with the TPS is pure coincidence. Go back and work your way through the TPS troubleshooter at the beginning of this post.

Code 85 - CANP solenoid - The Carbon Canister solenoid is inoperative or missing. Check vacuum lines for leaks and cracks. Check electrical wiring for loose connections, damaged wiring and insulation. Check solenoid valve operation by grounding the gray/yellow wire to the solenoid and blowing through it.
The computer provides the ground for the solenoid. The red wire to the solenoid is always energized any time the ignition switch is in the run position.

87mustang4001 · Nov 6, 2010

Thank you jrichker. Did just that and found the a crack in the line by the canister. I replaced it with a hose union. Problem is fixed.

83GL50 · Apr 8, 2011

I'm new to the site but I have read this on many other sites.
Well I checked mine and it was at 1.48v.Before I adjusted it wouldn't idle when cold for the 1st min and when it was warm it'd idle at 1000-1100 RPM.Also your eyes would begin to melt after a 1 min in the garage from it running so rich at idle.
After adjusting it to .93v cold the cold start idle was fine...no help to keep it running.The RPM's came down to around 750 when warm and now your eyes only want to melt after about 5 min of idling in the garage.

To me I believe it is very important to make sure it's with in range.

I wondering tho,is it the EEC adds 2.71v for WOT to the .93v = 3.61v or is it in WOT at 2.71v?
My base is .93v and with the throttle wide open I'm getting a 4.53v reading.Should it be this high?

This is all measured from the green and black wires on the TPS.

Mustang5L5 · Apr 8, 2011

83GL50 said:
I wondering tho,is it the EEC adds 2.71v for WOT to the .93v = 3.61v or is it in WOT at 2.71v?
My base is .93v and with the throttle wide open I'm getting a 4.53v reading.Should it be this high?

This is all measured from the green and black wires on the TPS.

It's 0.93 + 2.71 = 3.61. So as soon as the voltage hits 3.61, the computer assumes you are at wot (or pretty close to it and adjusts timing/fuel accordingly). Of your idle voltage was 1.00, this number would now be 3.71.

Anything beyond that makes no difference. Once you are over that voltage, you are technically wot and going to 4.5v makes no difference. It's normal

But yes, at idle, the voltage needs to be somewhere in the 0.5-1.1v range. But hunting for a specific number is not necessary. Last time I checked my voltage, I think it was set about 0.76v or somewhere in that range.

Adjusting the tps with the car running will always change the way it runs. After all, the engine has been started and the computer thinks you are manipulating the throttle and is adjusting air/timing...so the engine will run a little stronger as you advance. When you shut the car down, everything you did flies right out the window pretty much

83GL50 · Apr 8, 2011

OkThx

This was all done with just the switch on but with the car cold.Because there is a slight diff in volt readings when it's hot to cold.

Maryland Stang · May 29, 2011

It's a good thing it doesn't matter. I tried to get mine to .99 and the best I could do was .94 or something. I said FI and left it there. It idles and runs fine like that.

Mustang5L5 · Sep 10, 2011

Mckenzie500 · Sep 13, 2011

This is one of the best posts I've seen on this forum..it's too informative..thanks.

Gearhead92 · Nov 22, 2013

So I adjusted the tps, and it is sitting ~0.806V....

But I am still idling around 1100rpm and I can't get it to go down....

Also, I currently have only one vacuum line going to the carbon canister....how many should there be?

Mustang5L5 · Nov 22, 2013

If there is no TPS code, you don't have a issue with TPS

2 vac lines to the charcoal canister. One line to the gas tank, and the other line into the intake manifold up front

90lxwhite · Nov 22, 2013

I once tried this myth but.. The bolt holes wouldn't line up when it was reading .9 volts

mikestang63 · Nov 22, 2013

back in the day we all used to open up the holes on the TPS because you HAD to get the voltage to 1. lol Then people realized the cars ran fine as long as it's within a range. I think they used to sell a device that was TPS adjuster or something like that- like the MAF voltage adjuster when you swapped out injectors and MAF''s.

Gearhead92 · Nov 22, 2013

I was getting a TPS code. So I got the TPS to read 0.806V and then disconnect the battery for 15mins....and still high idle. Not as bad though. It was continuously around 1500rpm, now it might hit 1500rpm, but stays around 1100rpm for the most part.

jrichker · Nov 22, 2013

Gearhead92 said:
I was getting a TPS code. So I got the TPS to read 0.806V and then disconnect the battery for 15mins....and still high idle. Not as bad though. It was continuously around 1500rpm, now it might hit 1500rpm, but stays around 1100rpm for the most part.

You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix.

It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 134,000 hits, which indicates it does help fix idle problems quickly and inexpensively.

92Vert50 · Oct 2, 2015

I am getting 2 volts on the orange wire and .35 volts on the green wire. I assume my TPS needs to be replaced. I have been through the rest of the crank/no start checklist and am down to this. I have spark and fuel pressure, but no fuel in the cylinders. I replaced the distributor so PIP is new. The failure was catastrophic with no warning. There was a bit of a rough idle before the problem occurred. I have a 92 5.0 with about 25,000 original miles and no mods.

Mustang TPS Adjustment - 0.999999v not necessary

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