1998 jeep wrangler TJ with a 4.0 manual five speed. I am idling too high and running rough. (asked about similar issue, trying to whittle it down) This happened overnight. I have replaced the OEM TPS with another Mopar OEM tps. Still getting P0123 error
Ground is good voltages five which is good, but the signal is running high 0.94, should be 0.86.
Any thoughts?
Thank you so much.
P0123 code is set when the voltage on the signal wire exceeds the voltage range of the TPS circuit for more than a couple of seconds.
So on that 5 volt TPS circuit the highest voltage on the signal wire should never be higher than 4.5 volts. If it gets higher than that for a couple of seconds the P0123 code is set.
You can look at the Freeze Frame Data from when the P0123 code was set to confirm that the TPS signal voltage exceeded 4.5 volts.
Then you can "back probe" the TPS harness connector's Signal Wire with a multimeter, DC Volts, 20 volt range, Key On, and slowly open the throttle plate while watching the voltage on the multimeter. Make sure it doesn't go over 4.5 volts anywhere between throttle plate closed and wide open throttle.
Maybe jiggle the wiring connectors at the TPS and at the computer connector as well as the harness between the two and watch the signal wire voltage on the multimeter to see if you're intermittently losing the computer Ground or if you have an intermittent short to Power on that signal wire somewhere that causes the voltage on the signal wire to go over 4.5 volts
Maybe even unplug the computer and look at the pins and connector for corrosion or other issues.
The TPS 5 Volts, TPS Ground, and TPS Signal, looks like they're all on the Black Computer connector. So are the computer Grounds and the Ground to the TPS from the computer is only as good as the computer's Chassis Grounds so look up those Ground Points and check them too.
My powerline is 4.05… My ground is zero and my signal should be 0.86, but it is 0.94.
The voltage signal spec at idle isn't one specific voltage. The voltage spec range at idle is above 0.26v but below 0.95v. You're within the specs at 0.94v (barely)
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One reason for being on the high side at idle is a dirty throttle body. Look in the throttle body bore for dirt or carbon on the throttle plate or in the bore itself which is preventing the throttle plate from closing as far as it should
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That would explain the high idle but wouldn't explain the P0123 code. Did you look at the Freeze Frame Data from when the code was set to see the TPS signal voltage at the time?
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Frankly, your issue sounds more like a vacuum leak than a TPS issue but you can clean the throttle body and clean the IAC valve/solenoid first to rule them out
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Then you can (Live Data) look at the fuel trims at idle and then again when holding rpms above 2500. is there a positive fuel trim at idle that goes down when you hold rpms at 2500 for a minute or so?
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That would point to a vacuum leak
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You can also disconnect the battery cables and while disconnected touch the positive and negative cable clamps together for a couple of minutes
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That should kill the KAM and force a TPS relearn that will take a few drive cycles for the computer to learn
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Anyway, 1st look at the freeze frame TPS data from when the P0123 code was set
Oh, I did the reset… And it didn’t do anything… Symptoms still remain 13 to 1700 with a TPS plugged in… As soon as I unplug it, there is a slight stall and then back to the 770s rpm.
I went through an entire can of carb, choke cleaner, through all the vacuum schematics, and I can say that I have tested all vacuum connections…
I still have the primary issue which is electrical and nature because I can unplug the TPS and have RPMs in the 770s. They do not move very much.
So frustrating
Your explanation is fantastic… I just don’t think that’s it. I’ve taken off the throttlebody, thoroughly, cleaned it, cleaned the IAC, the only code I get is P0 123.
I’m very frustrated because I think that as soon as I take it to a shop they’re going to say well. It needs a new loom, well it needs a new computer, well, it needs a new throttlebody, well, it needs a new jeep.
ugh