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Throttle Position Sensor (TPS) Testing, Replacement and Adjustment

I chose not to post this under the "Ultimate Throttle Position Sensor Thread" and monopolize space as this is long and somewhat detailed. But I hope others can find this information helpful. Lots of specs, tips and pics.

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I was having a hunting idle issue along with a hesitation on acceleration and after transmission downshift. I pulled Diagnostic Trouble Codes and all I could find was a DTC 334 (EGR closed valve voltage high). My EGR was clean and visually controlled by the PCM, EVR and EVP tested good. My Idle Air Controller (IAC) was new and I had recently installed all new Silicone Vacuum Lines that repetetively tested good as well.







I then decided to test the Throttle Position Sensor (TPS). As a side note, back probing the TPS Harness Connector is challenging to get both probes to contact at the same time. It was then extremely difficult to hold the DVOM probes in place while manipulating the throttle. I am not a fan of piercing the wires with pins due to damage or future corrosion of the wires. At any rate, the values that I am looking for are as follows:

KOEO TPS Values
KOEO TPS Reference Voltage - 5v
KOEO TPS Signal Voltage - <1v to <4.8v
Unplugged TPS Resistance - <4k ohms to >350 ohms


KOEO TPS Testing
KOEO TPS Reference Voltage - VREF and SIG RTN
KOEO TPS Signal Voltage - TP SIG and SIG RTN (while rotating Throttle)
Unplugged TPS Resistance - TP SIG and VREF (while rotating Throttle)





Before testing, I first had to remind myself of the proper wire colors. They are as follows:

1988-1991 TPS Wire Colors
VREF - Orange/White
TP SIG - Dark Green/Light Green
SIG RTN - Black/White (My 1990 is actually Red/Gray)


1992-1996 TPS Wire Colors
VREF - Brown/White
TP SIG - Gray/White
SIG RTN -Gray/Red


Motorcraft TPS Wire Colors
VREF - Orange
TP SIG - Green
SIG RTN - Black







I found that I had good Reference Voltage of 4.78v but the Throttle Body Closed Resistance was only 3.01k ohms. Upon opening to Wide Open Throttle (WOT), I was only receiving 299 ohms which is outside of acceptable values. I had a difficult time in performing the important TPS Signal and VREF Resistance Throttle Rotation Test due to not having any assistance. The proper way to do this test is with an analogue Multimeter as a digital DVOM has an inherent delay in indicating dead spots during Throttle rotation. Regardless, either tool will work for this specific test considering an analogue Multimeter would be more responsive for the lesser trained mechanic.







Knowing that my TPS was not performing as expected, I purchased a new Motorcraft TPS (PN E7TZ-9B989-D (CX-1228)). The resistance tested at 3.75k to 356 ohms so I new that the old one was suspect.







Now I am ready to begin. First I removed the Throttle Cover to expose the Accelerator Cable and the Throttle Mounting Bolts...







Then I removed the Throttle Cable by prying it upward with a screwdriver...





I disconnected the IAC and the TPS Harness Connectors and began to remove the Throttle Body...







My BBK 56mm Throttle Body is attached by four ARP 1/4" hex bolts, but 6mm hex should work just fine. The upper Throttle Body Coolant Bypass Line and Canister Purge Solenoid (CANP) Line came off easily, but the lower TB Coolant Bypass Line was a challenge due to it's location. I decided to simply disconnect the lower Coolant Bypass Line at the Engine Coolant Temperature (ECT) Tee on the Intake Manifold instead. I stopped the coolant flow by first opening the Radiator Cap to release pressure and then installing a rubber Vacuum Line Cap on the tee.







After removing the four Throttle Body attachment bolts, off it came and I was in business.





Next was time to clean the TB with Throttle Body Cleaner. It was not very dirty but I did pay special attention to the Butterfly Valves and contact surfaces to prevent a sticky throttle plate. While I had the Air Tube off, I also carefully cleaned the MAF Sensor with Mass Air Flow Sensor Cleaner. Now would be a good time to replace or clean your IAC, but mine was almost new with no signs of contamination. If you do clean your IAC, remember to use only Carburator or TB Cleaner and avoid the sensitive Electrical Solenoid. Here it is, all clean...









Now for the task at hand. The TPS is attached at the base of the Throttle Body by two screws. Note the orientation of the harness for future install as some are orientated in different directions. The EEC-IV TPS is self-calibrating but the older pre-EEC-IV TPS may be adjustable by indication of oval screw mounting holes. If this is the case, you would then need to scribe the position of the TPS to the TB for a good base starting point.





After removing the TPS, I compared the new and the old. Note the shim ring on the old TPS and not on the new. When I mocked fitment of the new TPS to the TB, I noted that it was very loose and difficult to align. Using a screw driver, I carefull removed the shim ring and installed it on the new TPS. Fitment and alignment was then perfect.







When aligning the new TPS, the tabs should be in contact with the TB Shaft Tang with the upper tab to the left side and the lower tab to the right side. The TB Shaft Tang will turn the TPS in a counter-clockwise direction (viewing from the base of the Throttle Body). This is why you install the TPS slightly retarded and rotate it clock-wise into contact position. It is spring loaded to always keep it in contact with the TB Shaft Tang upon return to idle. Wiggle the TPS a bit to ensure that it is seated correctly and install the screws.







Ensuring a clean TB mounting surface, reinstall the TB using an inexpensive new Throttle Body Gasket (Felpro PN 60845) to prevent a vacuum leak. A little tricky as you will need to maintain gasket alignment by using the two upper TB Mounting Bolts. Do not use Edelbrock Gaskacinch or other gasket adhesive.







Once I had the TB reinstalled, I checked the TPS Signal Voltage and found .758v at Closed Throttle. This should be fine as my 1995 PCM is looking for at least .65v. The Factory Self-Calibrating TPS Range is as follows:

TPS Settings
1990 Bronco 4.9L - 0.73v to 1.22v
1990 Bronco 5.0L - 0.73v to 1.22v
1990 Bronco 5.8L - 0.73v to 1.22v
1995 Bronco 4.9L - 0.65v to 1.28v
1995 Bronco 5.0L - 0.65v to 1.28v
1995 Bronco 5.8L - 0.65v to 1.28v






I reinstalled the Air Intake and MAF Sensor, then I disconnected the battery with headlights on to erase any adaptive memory. When I reconnected power and started the engine, the PCM clearly was searching for good idle parameters. After 15 minutes idle, a test drive showed a good low end but a "heavy" feeling WOT. I know it takes time for the PCM to readapt, but the hunting idle was still there.

Time to retest the TPS to see if anything had changed. But first, I was tired of digging with the DVOM probes to back probe the harness connector. I remembered that I had once procured an old TPS Harness at the Junk Yard after seeing a post by broncoflorida. I had to dig for a while, and then I finally found it!!! Thanks BF!!!

I cut, spliced and soldered the wires to make a handy TPS Test Harness that would make this much easier, especially when working by yourself and trying to open the Throttle. (Note to self: get alligator clips for even easier use). :thumbup









After easily installing my new custom TPS Test Harness, here are the values that I received:

4.93v Reference Voltage - Good.



.758v Closed TB Signal Voltage - Good.



Mmm... The TPS Closed Throttle Body Signal Voltage is very close to the base parameters. Could this be a problem if it dips under tip-in? I decided to adjust my TPS to more center it within specifications.

First, I once again removed the Air Intake and Throttle Body. After wiggling the TPS to ensure that it was seated correctly, I removed the sensor and used a drill to elongate the TPS screw mounting Holes. Be sure you elongate the correct direction, bottom of the left side and top of the right side, in order to rotate the TPS slightly more clock-wise to increase voltage.





I then reinstalled the TPS with loosely torqued screws and layed the TB on top of the engine. After reattaching my TPS Test Harness, I retested with KOEO. This took three attempts, each time enlarging the TPS screw holes a little more and retesting on the Throttle Body connected to the harness. I finally achieved this:

.983v Closed TB Signal Voltage - Good!



4.61v Open TB Signal Voltage - Good!




I reinstalled everything and tested once more...

.981v Closed TB Signal Voltage - Great!



4.61v Open TB Signal Voltage - Great!




My TPS was now adjusted away from the edge of the lower tip-in value. After once again disconnecting the battery with headlights on for 30 minutes to erase any adaptive memory, I started the engine and let it idle for 15 minutes to allow the PCM re-establish a relationship with the new sensor. I took it for a drive and then tested for Diagnostic Trouble Codes.






Surprise! No more hunting idle, no hesitation on acceleration or after transmission downshift and the power was now smooth and light! And the exhaust smells better too!



Lessons learned:
  • EEC-IV TPS is self-calibrating, but stay away from the edge of setting specifications. In other words, centering is good.
  • Always completely test your TPS for Reference, Signal and Resistance.
  • A home made TPS Test Harness is worth it's weight in gold!!!
  • Use the opportunity to clean your Throttle Body, IAC and MAF.
  • It takes time for the PCM to fully adapt to the new TPS. Give it substantial idle and driving time.
  • Remember your Idle Mixture and IAC are non-adjustable as they are controlled by the PCM. Adjusting your TB Idle Adjustment Screw will cause a rich condition forcing the PCM use the limitations of the IAC to "hunt" for the programmed idle.


Time for a beer... :beer





For more information see this link: Throttle Position Sensor Management
 

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  • Remember your Idle Mixture and IAC are non-adjustable as they are controlled by the PCM. Adjusting your TB Idle Adjustment Screw will cause a rich condition forcing the PCM use the limitations of the IAC to "hunt" for the programmed idle.
I have been hunting a problem since I got my truck where when it starts up after warming up in P the idle goes up and down until it finds the right rpm range then for the most part settles down. When you say the PCM uses the IAC to "hunt" for the programmed idle because the tb idle has been possibly messed with, is the "hunt" you speak of where the idle is erratic? Here is a video I took of it doing a very slight hunt. Sometimes it is drops to 500rpm and shots up to 1100rpm and then bounces back and forth till it settles down.

From 2010..
http://www.youtube.com/watch?v=8agCDS3kGMo
 

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Hi Seattle FSB, as you know I followed your how to and replaced my TPS, cleaned my throttle body..etc and my Bronco is running excellent. I just wanted to add one thing and was hoping you could edit it into your how to section to help others. I noticed on my throttle cable assembly another cable, I think it might be the kick down cable, not for sure, but to remove it if you just pry up on it, you could possibly break the plastic attachment. What you need to do is pull forward on the plastic clip, and not pry up. If you notice in the photo the groove/slot where the metal tab will slid through. So I took 2 photos of how it is attached, to help others out, let me know what you think. Thanks, Joe
 

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I bought the fiveologyracing TPS calibration tool myself and the quality is very good and worth every penny IMO if you don't have time to go to the JY and make your own...:doh0715:

Good Luck ~ :thumbup
 

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I've been thinking about this and looking at the plastic piece for the stud regarding the TV cable, you could probably crimp on a metal " wire loop" in an electrical fix it kit to fit on/over the stud as long as you measure it so it's at the correct adjustment length......:doh0715:

Good Luck ~ :thumbup
 

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I tested my TPS earlier, and the resistance was 1100 ohms closed, and 4200 ohms at WOT. This meets the values for resistance, but resistance climbs as the throttle is opened. Is this normal, or is mine bad?
 

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Discussion Starter #11
Unplugged TPS Resistance needs to be fairly close to <4k ohms with TB normally closed and >350 ohms with TB manually opened. You are outside of these parameters, if you are testing correctly. Confirm with voltage readings by back-probing the plugged in sensor.

Remember the sensor pins you are testing are opposite (mirror) of the connector pins that the manual schematic shows. Look at the wire color reference that I listed for confirmation you are testing the correct pins. And be sure to use an Analog meter.
 

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Discussion Starter #13
I tested my TPS earlier, and the resistance was 1100 ohms closed, and 4200 ohms at WOT. This meets the values for resistance, but resistance climbs as the throttle is opened. Is this normal, or is mine bad?
TPS Resistance Testing is normally done on the unplugged TPS on the TPS SIG and VREF wires. You are looking for resistance values of <4k ohms at closed throttle and >350 ohms at WOT.


When testing resistance on the TP SIG and VREF wires, the resistance will decrease.

When testing resistance on the TP SIG and SIG RTN wires, the resistance will increase.


This is due to the design of the sensor and direction of the internal "wiper" that mechanically changes resistance. Depending upon which side of the TP Signal wiper you are testing (VREF or SIG RTN), the resistance will either decrease or increase with the counter-clockwise rotation of the sensor. The specification listed is for the VREF decreasing value.


Although resistance can tell us the condition of the sensor, our end goal is always the resulting voltage range being processed by the EEC.






For more TPS information, see this link: Throttle Position Sensor Management
 

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Eric
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This thread just helped me. I've been having hard-start, hunting idle, and "chugging" at freeway cruise between 1,500 and 1,900 RPM. Tested the TPS resistance, on a wild hair after reading this, and got ~160 ohms at WOT. Closed throttle checked out, though. Time for a new TPS.

My Haynes and two Ford tech manuals don't have the testing information/numbers for the TPS, so, this info. was, particularly, helpful.

Thanks Seattle. :thumbup

Eric
 

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I then decided to test the Throttle Position Sensor (TPS). As a side note, back probing the TPS Harness Connector is challenging to get both probes to contact at the same time. It was then extremely difficult to hold the DVOM probes in place while manipulating the throttle. I am not a fan of piercing the wires with pins due to damage or future corrosion of the wires. At any rate, the values that I am looking for are as follows:

KOEO TPS Values
KOEO TPS Reference Voltage - 5v
KOEO TPS Signal Voltage - <1v to <4.8v
Unplugged TPS Resistance - <4k ohms to >350 ohms



KOEO TPS Testing
KOEO TPS Reference Voltage - VREF and SIG RTN
KOEO TPS Signal Voltage - TP SIG and SIG RTN (while rotating Throttle)
Unplugged TPS Resistance - TP SIG and VREF (while rotating Throttle)

I've got a question for you Seattle, where do you get these value numbers? I would love to have this information as a reference when ever I'm tracking down issues. Also, I wanted to take the time to thank you for these very detailed and clear write-ups.
 

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Discussion Starter #17
where do you get these value numbers?
Start by buying a Haynes Manual and a Chilton's Manual. Then buy a Ford Shop Manual, Ford Engine/Emission Diagnostics Manual and Ford Electrical & Vacuum Troubleshooting Manual. And remember, the internet is your friend.
 

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I am having similar issues. 90 5.0 EB

I used seafoam by removing the lower intake tube inserting the spray tube as shown on the package 1/4" from butterfly valve.

About 50 miles later it started running rough. Then cut out a few times. I did find my fuel pump gave out and my plugs were fouled.

Replaced parts:
Fuel pump (couldnt hear it anymore) and filter
Plugs - they were really bad
Ignition coil- neighbor that helped me said the spark looked weak
Dizzy cap and rotor
Plug wires were done less than 2k miles ago

After reading a lot on here I can't find anyone that used the aerosol form of seafoam and used it in the way I did. I'm guessing spraying into the lower intake tube has caused tps to fail.

Can anyone with more experience concur with that?
 
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