TPS & Base Idle Reset

Fri Guy · May 16, 2025

Planning on doing a base idle reset soon. I've seen and read the whole process of it. But the one thing I am not certain about is where to place the leads of the volt meter on the TPS. Can anyone tell me exactly where I should be placing the leads?

91AOD5.0LX · May 16, 2025

Watch this video from LMR starting at 1:20 on the counter. Bottom line is Red lead from the volt meter to the green TPS wire using a sewing needle then the black lead from the meter to ground.

View: https://m.youtube.com/watch?v=HUwr0g5Qn7s

Fri Guy · May 16, 2025

Thanks man.

Mustang5L5 · May 16, 2025

There's no need to adjust the TPS voltage. It's considered non-adjustable as the ECU uses an algorithm to take base voltage on startup and assign it a value. Dialing it into 0.99 doesn't really accomplish anything. The true range is 0.5 to 1.25 volts.

Now if you want to verify voltage, there's no harm in that

Thread 'Mustang TPS Adjustment - 0.99v not necessary'

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. This is a Ford internal Doc (don't ask how I got it)

Pay attention to the part highlighted in yellow. I've posted a few more snips of the ECU GUFB related to TPS strategy in post #42 that highlight the ladder logic.

So with that said, adjusting your TPS to .99999999 volts is not necessary at all. The ECU has a...

Fri Guy · May 16, 2025

Thank you. So basically go through the base idle reset without messing with the TPS?

Mustang5L5 · May 18, 2025

Yup. I haven’t measured a TPS in years. Couldn’t ever tell you what mine was set to when I had the stock ECU.

Fri Guy · May 18, 2025

When you disconnect the TPS sensor with the car running shouldn’t the idle drop down? We tried it on my buddies car and the idle didn’t change at all. He is having idle issues and surging.

JMG9350 · May 18, 2025

The IAC controls the idle speed, not the TPS

Mustang5L5 · May 18, 2025

TPS is not really a primary function in terms of engine management. It has its purpose but for it to have a significant role would require a few other sensors to completely fail first.

Really it just tells the ECU two things. Idle, and WOT.

Unplugging it would trip a code, disable the tps function. Would the idle drop? It really all depends on other variables so it’s not really a strong measure of function.

You can certainly hook up the meter and test the tps for full range, dead spots, not moving above idle, etc, but you don’t need to go crazy adjusting it. If it’s sitting at 0.51v maybe you might want to bump it up a bit to mid range to account for wire resistance changes due to temps.

Fri Guy · May 18, 2025

I apologize, I meant the IAC. When we unplugged it the idle did not change at all.

General karthief · May 18, 2025

The biggest cause of idle issues are vacuum leaks.
IAC will be unable to do it's job, vacuum leaks will render it useless, give your friend the 'surging idle checklist' just make sure he reads and follows the instructions (after all, we are MEN, right?) Otherwise you could be chasing you tail.

Fri Guy · May 19, 2025

Thanks, going to try using smoke to check for leaks. Will use the surging idle checklist and see if we can find out what the issue is.

Mustang5L5 · May 19, 2025

Fri Guy said:
I apologize, I meant the IAC. When we unplugged it the idle did not change at all.

Most likely your throttle stop screw is set to high.

Unplug the IAC, and then turn the throttle stop screw to close the throttle blade. Drop it down as low as you can get it where it will still idle pretty steady.

THEN you reset the ECU to perform the base idle reset.

Sometimes if the idle stop screw is set with the blade too far open, the IAC stays closed and does nothing to regulate idle because it wants idle to drop. Then you get an inconsistent idle. By closing the blade down, most of the idle airflow is through the blade and the IAC can then just fine tube the idle by barely opening.

Fri Guy · May 19, 2025

Thanks.

Dontknowchit · May 20, 2025

I recently did this with the addition of pulling the spout. Ran up to operating temp, pulled spout and IAC and adjusted throttle stop screw to around 650-700 anything stable in that range. Shut off, replug sensors, key on, reset TPS, all was good again. Theory goes that if you don't pull spout, computer will be trying to adjust timing while you adjust throttle screw. Have to pull timing control away from ecu while making the adjustments. Also, resetting TPS is not always necessary, but it can be if you are too far out of spec. The whole .98 thing is just to be in the mid point of the range of readable values. Depends on how much monkeying you have been doing with it and if you are running a stock TB.

JMG9350 · May 20, 2025

The computer doesn't care about the TPS voltage as long as during the initial key on it's somewhere within .5 to 1.25 volts. Your idle is too high with the IAC unplugged. The computer wants to be able to control the idle with the IAC at around 30% duty cycle, and the computer is programmed to want to idle at 672 RPM. This is why custom tuning is necessary to achieve a smooth idle at a higher RPM if you have a big cam. There are functions in the computer that need adjusted to achieve that, and not upset it.

Mustang5L5 · May 21, 2025

Forgot to mention pulling the spout. Good call

Noobz347 · May 21, 2025

Dontknowchit said:
I recently did this with the addition of pulling the spout. Ran up to operating temp, pulled spout and IAC and adjusted throttle stop screw to around 650-700 anything stable in that range. Shut off, replug sensors, key on, reset TPS, all was good again. Theory goes that if you don't pull spout, computer will be trying to adjust timing while you adjust throttle screw. Have to pull timing control away from ecu while making the adjustments. Also, resetting TPS is not always necessary, but it can be if you are too far out of spec. The whole .98 thing is just to be in the mid point of the range of readable values. Depends on how much monkeying you have been doing with it and if you are running a stock TB.

So, now you know something and have to come up with a new screen name.

General karthief · May 21, 2025

Noobz347 said:
So, now you know something and have to come up with a new screen name.

How 'bout Don'twanttoknowchit?
Or Ialreadyknowchit?

Dontknowchit · May 21, 2025

Noobz347 said:
So, now you know something and have to come up with a new screen name.

Only regurgitating what I learn here from y'all

TPS & Base Idle Reset

Fri Guy

91AOD5.0LX

I have a slight sag in my rear

Fri Guy

Mustang5L5

That is…until I whipped out my Bissell

Thread 'Mustang TPS Adjustment - 0.99v not necessary'

Fri Guy

Mustang5L5

That is…until I whipped out my Bissell

Fri Guy

JMG9350

Active Member

Mustang5L5

That is…until I whipped out my Bissell

Fri Guy

General karthief

wonder how much it would cost to ship you a pair

Fri Guy

Mustang5L5

That is…until I whipped out my Bissell

Fri Guy

Dontknowchit

Active Member

JMG9350

Active Member

Mustang5L5

That is…until I whipped out my Bissell

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

General karthief

wonder how much it would cost to ship you a pair

Dontknowchit

Active Member

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wonder how much it would cost to ship you a pair

That is…until I whipped out my Bissell

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Stangnet Facilities Maint Tech... Er... Janitor

wonder how much it would cost to ship you a pair

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