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Old 03-25-2011, 01:47 PM   #1
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Having problems with MPG? It could be your TPS.

Over the past year I have had diminishing fuel economy in my 2004 LJ. 14MPG tops with no regard to city or highway. While going up hills the wrangler would roar in 2nd gear while struggling to summit. It idled a bit high while decelerating too. On a long road trip the Wrangler would alternately refuse to accelerate up a hill, or refuse to upshift down a hill.

I though my transmission was going out. The 42RLE was the only option for Unlimiteds in 2004 and I am still kicking myself for not waiting one more year for the new 6 speed. Hindsight aside, after going to my local transmission shop they said the 42 was in tip top shape. I guess its always kinda underpowered and lame.

The problem was found in an Power Control Module (PCM) test. My throttle indicated a max of 85% while floored, and a min of 5% when under no pressure whatsoever.

My Throttle Position Sensor (TPS) was malfunctioning.
Going to post a basic Write up that I'm sure is waaay to simple for most guys on this forum. But I hope to do more complex ones in the future, and this might help those that don't know this can be an issue.
Here we go!

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Old 03-25-2011, 01:48 PM   #2
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Description:
The TPS is a variable resistor that tells the PCM the throttle position (duh). What I did not know was that it controls fuel injector pulse and ignition timing. It adjusts idle settings, deceleration fuel lean out, fuel cutoff during cranking, and some features of the auto tranny. In other words all of my Wrangler's infuriating behavior was caused by this little bugger.

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Old 03-25-2011, 01:49 PM   #3
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In labor it'd cost around $190 to replace a $50 part. I just can't justify that so I went and did it myself. EASY FIX!
All you need is a set of Torx keys and a wrench for your battery cable.


Purchase the appropriate TPS for your model year. Mine was found at the RockAuto Parts Catalog
Specify your model year, I'm pretty sure they change parts just for fun from year to year.
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Old 03-25-2011, 01:50 PM   #4
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Here are the simple steps you'll need to fix this problem:

1: Disconnect your battery. This is not just for safety. While you are installing your TPS the PCM's memory will clear. This will cause it to unlearn all the bad behavior it has gotten into by listening to your errant TPS. It takes 20 minutes or so for this to happen, and about that long to do the install.
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Old 03-25-2011, 01:50 PM   #5
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2:Locate the TPS on your throttle body. Here's a schematic:
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Old 03-25-2011, 01:53 PM   #6
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3: Remove your air cleaner tube from the throttle body, you don't have to but it makes it way easier to get to.
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Old 03-25-2011, 01:53 PM   #7
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4: Disconnect the plug from the TPS, and remove the mounting screws. Mine were torx screws, like everything Jeep, so you'll need a set. Allen keys sorta work, but can strip the head.
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Old 03-25-2011, 01:54 PM   #8
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5: Throw your TPS away, burn it, crush it, swear at it, dousing it in gasoline seems appropriate. I just threw mine in a corner to let it think about what it had done.
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Old 03-25-2011, 01:55 PM   #9
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6: The Throttle shaft (See figure 2) slides into the slot on your new TPS. You have to slightly rotate it so it sets properly, when you put it into place it'll be under light tension due to this necessary rotation.
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Old 03-25-2011, 01:55 PM   #10
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7: Tighten the torx screws, plug the TPS back in, re-install the air cleaner tube.

8: Be sure to check that there is no binding by hand checking the accelerator at the throttle body. If there isn't you are set!
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Old 03-25-2011, 01:56 PM   #11
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9: Reconnect your battery, it will take 200 miles for the PCM to relearn the proper TPS settings. You may not notice an instant change in fuel economy, but you will get way better throttle response.
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Old 03-25-2011, 01:57 PM   #12
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After that you'll see better economy and better behavior uphill. I'm getting 17 avg mpg now! That 's mostly in traffic so its pretty good!

Hope this helps someone out!
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Old 03-25-2011, 01:57 PM   #13
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How did you test the Power Control Module, I have a stock 2005 LJ thats having the same MPG issue, my 33's on my TJ with 4.88's get better mileage!
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Old 03-25-2011, 02:01 PM   #14
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Oh yeah: I need to add that I am not responsible for any death or dismemberment you may encounter while doing this project. I have no idea what kind of trouble you may get into with a set of allen keys and a wrench, but I am not to blame. Lame that I need to state that. Reminds me of the time I had to tell an ebay buyer that the motorcycle I was selling did not include the bicycle in the photo behind it. What a world.
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Old 03-25-2011, 02:02 PM   #15
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The transmission shop I went to tested it for me for free. The testing module itself cost as much as my Jeep.
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Old 03-25-2011, 02:05 PM   #16
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Oddly, the PCM did not throw any codes. The shop checked the TPS by pressing my accelerator to the floor with the engine off. The tester showed 85% throttle, despite being maxed out.
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Old 03-25-2011, 02:06 PM   #17
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Because it wasn't a transmission problem, there wasn't anything they could do for me. That's when I researched doing it myself.
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Old 03-25-2011, 02:11 PM   #18
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Thanks, I'll look around.
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Old 03-25-2011, 02:13 PM   #19
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i wonder if this would be my issue. My MPGs are alot like the roller coasters at Six Flags. I can have a 16.5mpg one week, then 14.8, 15.4 the next week. Driving along the same route to and from work, driving the same way as far as the skinny pedal goes, and using the same gas. Last week i got a whopping 14.4mpg, this week, im sure im already above 16 again. With me being OCD as to where the gas needle is after X amount of miles, it drives me crazy. I know i dont get good mileage, i get it... its a jeep. But consistency would be nice. But whatever, right now, i just drive it, and fill it up when it needs to be.
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Old 03-25-2011, 03:04 PM   #20
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I had the same issue for a long time before it finally got 14mpg all the time. Could be the TPS going out, could be lots of other things. See if a local shop will test it for you. For the price of one tank you can buy a new TPS.
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Old 03-25-2011, 05:06 PM   #21
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Quote:
Originally Posted by young-blood View Post
For the price of one tank you can buy a new TPS.
What kind of tank?..

If you TPS is bad, hopefully it will leave an error code in the PCM that will show up on a free scan. You can also test it with a volt/ohm meter. I had some weird drivability issues on my old 93xj that I eventually traced to the TPS after trying lots of other stuff.
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Old 03-25-2011, 06:52 PM   #22
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Quote:
The problem was found in an Power Control Module (PCM) test. My throttle indicated a max of 85% while floored, and a min of 5% when under no pressure whatsoever.
I'd really like you to go back and have them test it again and report the new values. I'm assuming they just used a scanner and pulled the throttle plate position in % from the PCM, maybe have a friend do it for you? I have a scanner that does the same thing

Long story short, my '02 has a range of about 8-75% on the throttle position, similar to yours. I replaced the TPS with 3 different ones and the range is always similar, even after multiple overnight battery pulls.
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Old 03-27-2011, 09:38 PM   #23
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I honestly hadn't thought of doing that. Everything has been working so well MPGwise since I replaced it. Hmmmm, next time I'm near a shop I'll check it out.
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Old 03-28-2011, 10:42 AM   #24
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85 and 5% is normal. Go test your new one and you will see similar values.
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Old 03-28-2011, 11:42 AM   #25
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I've seen others report much better values, like 3-95, IIRC mine was more in the 8-75 range
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Old 03-28-2011, 02:05 PM   #26
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Where did you get the TPS? I need one (my Jeep throws a P0123 code every few weeks) and I mail-ordered one from Crown. It fit on the throttle body just fine, but the pin spacing on the electric plug was wrong, the harness would not plug in. Some parts books claim the same part for '97 to '06, while others list one just '97 to '02. My guess is the plug changed in '03 and you found the part I need for my 2003.

Gary
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Old 03-29-2011, 02:31 PM   #27
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Old 03-29-2011, 02:39 PM   #28
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BTW, I have not checked what my new throttle position %s are.
But I don't see how it matters, as this check led to transmission guy to recommend I replace the TPS. My fuel economy has increased and my difficulty getting up hills without odd behavior from the transmission are now gone. Nothing else has changed, so the TPS was the likely culprit. What else would it be? So I gotta admit, I don't know why my numbers were supposedly "normal," but replacing the TPS was my solution and those numbers were the reason I replaced it.
Like I said, I'll check into the %s when I can, but right now I'm just happy the MPG problems were solved. So until something else goes wrong, I dont want to upset what my dad called "the balance of shi**yness" further by second guessing a good thing. LOL
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Old 03-29-2011, 02:52 PM   #29
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I will back this one up from real world experience. I noticed a pretty big decrease in mileage right after installing my lift. I was baffled for a couple weeks until I was on my way to work and the Jeep started bucking a bit and threw a code. Peplaced the TPS as the code indicated and MPGs returned to normal.

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Old 03-29-2011, 03:04 PM   #30
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Bada bing!
Basically same thing here, I just took a lot longer figuring it out as I hadn't saveda code for some reason. The check engine light did flash once, but went out again before I could read it. Have no idea why.

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