tps test

just did a tps test on my 97 xj, I am showing 5.12 volts at idle and 5.11 at wot. is this bad??

Probably. The TPS should show low voltage at idle. The TPS is routine maintenance item that is replaced when it wears out or tests out of specification. Buy a quality replacement from NAPA or Jeep. Cheap replacements often test faulty right out of the box.


You should have 5 volts going into the TPS. At wide open throttle (WOT), TPS output voltage must be less than 4.5 volts. The best is to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts. One of the other wires should show at idle, TPS out put voltage greater than .26 volts but less than .95 volts. The other wire will be the ground and should show no voltage. Move the throttle and look for smooth meter response up to the 4.49 at WOT.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.

Well, I don't know--let me look:

From the 97 FSM:

With the ignition key in the ON position, check the TPS output voltage at the center terminal wire of the connector. Check this at idle (throttle plate closed and at Wide Open Throttle (WOT). At idle, TPS out put voltage should be greater than .26 volts but less than .95 volts. At wide open throttle, TPS output voltage must be less than 4.49 volts. The output voltge should increase gradually as the throttle plate is slowly opened from idle to WOT.

Yep, it would seem it is bad.

That's assuming he's measuring the correct pin. Sounds like maybe he's measuring the supply voltage to the TPS? How do the other pins measure?

lawsoncl said:

That's assuming he's measuring the correct pin. Sounds like maybe he's measuring the supply voltage to the TPS? How do the other pins measure?

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3 wires, give you 3 wire combinations to read across, one pair is a flat line at a steady voltage from idle to WOT. He read across that pair, the wrong pair or from the 5 V input to ground.

he needs to find the pair that reads under 1 volt, then test that same pair at WOT. I forget the ABC combo, and it maybe different on 90's anyway.

Hi,

Bringing up an old post I found on TPS.

The other day I was driving on the interstate and took my foot off the gas pedal to begin slowing down for an exit ahead. The engine revved up probably 750RPM to about 3500. Then it did it again, and then on the off ramp it was somewhere about 1500RPM instead of 750-1100 RPM. It then seemed to be fine and hasn't happened since.

This has never happened before that I can remember.

I did this TPS test, but I did as Ohm meter test with the connector disconnected and only a digital gauge. The ohms seem to move fine with no dead spots. However, the ohms at idle can vary between 4.5-4.8 ohms (on 20K scale). Tapping the TPS WILL always make the idle value change. However, at various throttle positions tapping does not change it even 0.01.

Am I chasing my tail on this with the TPS? Is the change at idle significant, or relatively insignificant?

At WOT, the values are consistent and do not change.

2001 XJ

I filed down a paper clip and was able to read voltage. Closed throttle/idle is 0.59-0.62V and WOT is 3.4V. If I flip the throttle back and forth the closed/throttle idle volts will change but only that 0.03. Tapping the TPS does not change the voltage read out. My 01 FSM says difference between idle and WOT should be at least 2.6V which I'm getting. With this additional test, can I conclude the TPS is probably fine?

Are you having an issue that leads you to think the TPS is bad....CEL, rough idle, stalling,etc?

md21722 said:

..... took my foot off the gas pedal to begin slowing down for an exit ahead. The engine revved up probably 750RPM to about 3500. Then it did it again, and then on the off ramp it was somewhere about 1500RPM instead of 750-1100 RPM.

Click to expand...

I would suspect a dirty or faulty Idle Air Controller. Clean the IAC. Replace the IAC if the symptoms persist.


Cleaning the Idle Air Controller (IAC) :

Purchase sensor safe Throttle Body cleaner spray.


1. Remove the Throttle body from the intake manifold.
2. Remove the IAC with a TORX 15 driver (2 bolts)
3. Gently wiggle out the IAC from the throttle body
4. Clean the IAC with Throttle Body Cleaner (not carburetor cleaner). Use cleaner, a rag, and a toothbrush. Be gentle; don’t twist or pull on the pintle as it is fragile and can be damaged easily
5. Also clean where the IAC seats in the throttle body with the same throttle body cleaner
6. While you have the Throttle Body off, give it a good cleaning also.
7. Reinstall IAC, the Throttle body, and check idle quality.

.

The CEL burned out a few years ago. I haven't checked for codes recently.

No stalling.

Idle is pretty good though occasionally it feels like its hunting a little bit (tach moves a needle width, if that).

Biggest reason I asked was this weird RPM surge when I took my foot off the gas at highway speed.

Second reason is most of the time the Jeep first right up, but occasionally (couple of times a week?) it requires cranking for a few seconds.

I'd think the idle is IAC but I was thinking that surge may be TPS related.

Thanks Tim, I removed the IAC (bolts were T-20 on mine), removed the shaft, and cleaned the head and sleeve down to bare metal. Also cleaned the throttle plate area down to shiny aluminum. Had a thin black oily residue below the throttle plate. I took it out for errands and it may idle a bit better now, was pretty good before, but barely see the tach move now. That was the first time any of that had ever been cleaned since the vehicle left the factory.

The problem occurred again on this morning, but a bit differently.

When I fired up the engine, it started OK at normal high idle then went to about 2000 RPM. Then it went back down in increments, like the computer was doing it.

On city streets it was fine, but a few miles on the interstate and I was back to surging when I took my foot off the pedal. Take foot off gas, engine slows down a little like normal, then goes up 750 almost like it's coming out of OD, then comes back down. Seemed to do this over 70MPH.

The idle first thing seems like IAC to me. What does the IAC when you're on the highway at speed?

Tim_MN said:

Replace the IAC if the symptoms persist.

Click to expand...

Seems like you need a new one.

The engine was starting to cut out on the way home. No surging this time. I bought a TPS at the dealer when I was there picking up my motor mounts. Stopped at Auto Zone after that and had 2 TPS codes for voltage. I may need IAC yet. I'll let ya'll know how this works out. Dealer TPS "Made in USA".

The logic of your post seems to indicate you think the TPS controls throttle blade opening. It does not, the 4 liter is cable driven, and it's just a computer input not an actuator.

However the IAC is a stepper motor and can directly effect throttle by allowing more air in.

I think Tim has you on the right path.

I knew the TPS was a sensor, not an actuator. I could never find any information saying the IAC affects at speed drivability, but I did see information that says the TPS affects transmission shifting.

I think the TPS resolved the problem, but will need another week or more to be sure.

I think my TPS had an intermittent problem when it got hot, like in warm weather on the highway, because the problem never occurred in town.

Keekleberrys said:

The logic of your post seems to indicate you think the TPS controls throttle blade opening. It does not, the 4 liter is cable driven, and it's just a computer input not an actuator.

However the IAC is a stepper motor and can directly effect throttle by allowing more air in.

I think Tim has you on the right path.

Click to expand...

A bad TPS can tell the computer to increase or decrease the fuel injector open time, and over or under feed fuel, causing wild swings in engine speed. So can a bad intake air temp sensor, at least on Renix years. A stick floor mat under the gas peddle can screw with the engine speed as well :smsoap:

I've driven about 800 miles with the new TPS and the problem has not come back.