IAB sensor disconnected

Did you reset the KAM after the adjustment? Otherwise if a high dwell was required before, that could be causing a long re-learn time.

FWIW, if you are SD, you set the idle with the IAC connected.

Good luck.

I would want to ensure there is no vac leak. ALso, do you have a hole in your TB butterfly?

Good luck.

TrophyHead said:

I'm reading 16-17 in-Hg on my engine vacuum. It's going up and down cause my idle is surging. Is this a good vacuum reading?

Got some of codes:

21- ECT out of range. Is there a way of adjustment to get it back into range or just replace the sensor.
23- TPS out of range
24- Intake air charge temp out of range. ACT sensor or IAT sensor? Do our cars even have an IAT sensor????
84- EGR vacuum regulator circuit faliure

Could somebody point me in the right direction as to where a ECT sensor is located and the ACT sensor?

I was talking to a mechanic at the local tire shop and he was talking about false engine codes from Frod to make the car owner not be able to fix his own car. Hence having to send it to a dealership(money making scam). Has anybody ever heard of this? I reliaze our OBC's are farily old. Is this a newer car thing or what?

As for the EGR promblem anybody know what can be at fault there?

Thanks for any help.

Click to expand...

That is an ok vac reading. FWIW, my stock SD cam gives 19.5" hg at idle. I still think you might have a bit of a leak somewhere. Seems to me that a leak on a SD car can start to give it a little surging.

For the ECT, JRichker has posted the values that sensor should read at various temps. However, it does degrade over time and is not very expensive to replace. Just make sure wiring to it is sound as that alone can lead to issues which a new sensor wont fix.
The ACT (or IAT) sensor is the same kind of sensor as the ECT (thermistorized. Word JR?). It also is cheap to replace. We dont have one in the intake.

I would dial in the TPS as I feel it does make a difference on SD cars (even on MAF cars, where it shouldnt make any difference, it can help).

JRichker has the master posts on figuring out the trouble codes - check his replies for those codes and answers.

Let me dig out a diagram from Tim with sensor locations. Back in a second.

Good luck.

Here is a diagram, courtesy of Tim (Stang 22). It might help with component locations.

Good luck.

Code 21 – ECT sensor out of range. Broken or damaged wiring, bad ECT sensor. Note that that if the outside air temp is below 50 degrees F that the test for the ECT can be in error.

The ACT & ECT have the same thermistor, so the table values are the same

ACT & ECT test data:

Use Pin 46 on the computer for ground for both ECT & ACT to get most accurate readings.

Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts. It is a good number if the ACT is mounted in the inlet airbox. If it is mounted in the lower intake manifold, the voltage readings will be lower because of the heat transfer.

Voltages may be measured across the ECT/ACT by probing the connector from the rear. Use care in doing it so that you don't damage the wiring or connector.

Here's the table :

68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .80 v
194 degrees F = .61

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.

Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.
50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms

Code 23 - Throttle sensor out of range or throttle set too high - TPS needs to be reset to below .99 volts at idle. Keep in mind that when you turn the idle screw to set the idle speed, you change the TPS setting.

Try this... Currently there is some dispute about setting it at .99 volts but anything less is probably OK. All you need is less than 1.0 volt at idle and more than 4.25 at Wide Open Throttle (WOT). You'll need a Digital Voltmeter (DVM) to do the job.

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

Here’s a TPS tip I got from NoGo50

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. Set it at .97v-.99v, the closer to .99v the better.

(copied from MustangMax, Glendale AZ)

1. 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.

2. 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.

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

4. Check the procedure for your year, on my 90 I have to turn the idle screw until it just touches the tab, then insert a .010 feeler gauge and give it about one more turn. Then you adjust the TPS voltage to .98v, reset the computer. Start it up, if the idle is to low then turn the screw in until it is just right, then readjust the TPS voltage to .98v and reset the computer and start it up. The key is to adjust the TPS voltage and reset the computer whenever the idle screw is changed.


If resetting the TPS doesn’t fix the problem, then you have a wiring problem with the TPS signal ground, the black/white wire that connects to pin 46 on the computer. With the power off, measure the resistance between the black/white wire on the TPS & the negative battery terminal. You should see less than 2 ohms. More than 2 ohms means a bad wire or bad connection. 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 2 ohms. Next check the resistance between the black/white wire and the negative battery post. It should be less than 2 ohms. Clean and inspect the 10 pin connectors too.



Code 24 - Intake Air Temperature (ACT) sensor out of range. Bad sensor, bad wiring. The ACT for Mustangs built before 95 is in the #5 intake runner. It measures the air temperature in the intake to help computer determine the proper air/fuel ratio.

Note that that if the outside air temp is below 50 degrees F that the test for the ACT can be in error.

ACT & ECT test data:

The ACT & ECT have the same thermistor, so the table values are the same

Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts. It is a good number if the ACT is mounted in the inlet airbox. If it is mounted in the lower intake manifold, the voltage readings will be lower because of the heat transfer. Here's the table :

68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .80 v
194 degrees F = .61

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.

Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.
50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms

TrophyHead said:

Thanks jrichker

I did most of those tests you sugest and everthing seems to be in range. I grabbed a nice meter at work. It's a Fluke 743B DPC it's a crazy meter. Still learning and reading how to use all the functions.

Click to expand...

I looked at Fluke's website and WoW! It seems that you can measure almost everything on a Mustang's electrical system using it. Have fun reading the manual...