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Old 06-02-2013, 02:30 AM   #1
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Loss of power/ rough idle..

So I have been having issues lately with my engine. I start my jeep up and it idles fine bit once I hit the gas and let go it will dip down to 250 rpm or completely die. Sometimes even when I give it gas instead of revving up it bogs down. I got a check engine light and the code that came up was p0123 which is too high of voltage in the throttle position sensor... So today I replaced the throttle position sensor and that has not fixed it, any other suggestions on what I should try next?
I have a 98 wrangler 4.0L

Thanks, Justin ZJ

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Old 06-02-2013, 02:54 AM   #2
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So I have been having issues lately with my engine. I start my jeep up and it idles fine bit once I hit the gas and let go it will dip down to 250 rpm or completely die. Sometimes even when I give it gas instead of revving up it bogs down. I got a check engine light and the code that came up was p0123 which is too high of voltage in the throttle position sensor... So today I replaced the throttle position sensor and that has not fixed it, any other suggestions on what I should try next?
I have a 98 wrangler 4.0L

Thanks, Justin ZJ
Clean the throttle body you might have carbon buildup also check air filter and intake tube... make sure there's no buildup of dirt etc.... also check intake manifold it might be clogged. My jeep had the same symptoms as your's and this fixed it....

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Old 06-02-2013, 07:50 AM   #3
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Have you reset the computer so it can relearn your new TPS? Also, if you bought it from an auto parts store rather than OEM, that too could be the problem.

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Old 06-02-2013, 10:41 AM   #4
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Cool I will definitely try cleaning all that stuff up for sure and as for the tps, I did reset the computer by disconnecting both terminals of the battery. (Is that how it's done? Or something else?) and I pulled the tps of another jeep. So I'm not sure if it is oem or not, how can I tell?
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Old 06-02-2013, 09:50 PM   #5
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I got a few suggestions that it may be a fuel filter, however my model doesn't have one it has a strainer that is attached to the fuel pump which is inside the gas tank. Does this sound like a possible option? I would like to know before I take on the task of dismounting my tank... Also it may be worth noting that it rained all day while I was at work the day before any of these problems occurred and I had my top off.
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Old 06-03-2013, 11:56 AM   #6
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No, disconnecting the battery cables will not reset the computer. You will need a "Code Reader," to reset any codes or the computer, and a drive of at least 60 miles for the computer to reread all the sensors. Once you disconnect the power the computer no longer communicates with the sensors and thus will need to relearn.
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Old 06-03-2013, 10:47 PM   #7
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So if I replace the part without resetting the computer it will still have problems until it has been reset?
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Old 06-11-2013, 07:31 AM   #8
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No, disconnecting the battery cables will not reset the computer. You will need a "Code Reader," to reset any codes or the computer, and a drive of at least 60 miles for the computer to reread all the sensors. Once you disconnect the power the computer no longer communicates with the sensors and thus will need to relearn.
So along same lines recently we installed 3 inch lift on my 2003. 4.0 rangler during this we accidently allowed battery to run down my local tech sez guna hafto run a wile so comp can relearn codes haz terrible ruff idle dies at every stop unless u do quick footwork to keep idle up. Thanxxx
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Old 07-17-2013, 06:47 AM   #9
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Set of new plugs Clean tps. And throttle body. New magnaflow xhaust system. Runnin. Great. Thanxx for evey bodyzzz suggestions.
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Old 07-17-2013, 09:31 AM   #10
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So along same lines recently we installed 3 inch lift on my 2003. 4.0 rangler during this we accidently allowed battery to run down my local tech sez guna hafto run a wile so comp can relearn codes haz terrible ruff idle dies at every stop unless u do quick footwork to keep idle up. Thanxxx
I know this is a late response but an engine running/idling poorly after the battery has been run down is the result of the battery voltage being too low to run the alternator, not from the computer needing to relearn the engine parameters. The alternator requires 12 volts from the battery so if the battery is too low, the engine either won't run at all or it will run poorly.

The days of an engine being able to run without a battery or with a dead battery once jump started are pretty much over for most vehicles. Most alternators used now do require 12 volts from the battery to work & if the alternator can't provide enough power, the ignition will either not work or not provide enough spark for the engine to run well. When that happens, it is best to use a true battery charger overnight to charge the battery bacj up to 100%. The alternator wasn't designed to and can't always recharge completely or nearly dead batteries.
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Old 08-11-2013, 05:53 PM   #11
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I know this is a late response but an engine running/idling poorly after the battery has been run down is the result of the battery voltage being too low to run the alternator, not from the computer needing to relearn the engine parameters. The alternator requires 12 volts from the battery so if the battery is too low, the engine either won't run at all or it will run poorly.

The days of an engine being able to run without a battery or with a dead battery once jump started are pretty much over for most vehicles. Most alternators used now do require 12 volts from the battery to work & if the alternator can't provide enough power, the ignition will either not work or not provide enough spark for the engine to run well. When that happens, it is best to use a true battery charger overnight to charge the battery bacj up to 100%. The alternator wasn't designed to and can't always recharge completely or nearly dead batteries.
Same issue, battery was fine no issues, went muddying, now my batter my battery gauge is at 0, the battery ran dead. I know the battery is good... But what do I do? Thanks!
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Old 08-11-2013, 05:58 PM   #12
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Could be that your alternator is packed with mud, flush it out with copious amounts of hose water followed by copious amounts of WD-40 to chase the water out, or your battery connections are loose or dirty/corroded. Disconnect them wire brush, then securely reinstall them & get the bolt tight enough so the connector cannot be moved or rotated at all by hand.
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Old 08-11-2013, 06:15 PM   #13
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I had a similiar problem. Ended up being my distributor cap connections were bad. Your distributor cap may have mud in it also which u should clean out maybe causing misfires
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Old 08-13-2013, 09:09 PM   #14
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Could be that your alternator is packed with mud, flush it out with copious amounts of hose water followed by copious amounts of WD-40 to chase the water out, or your battery connections are loose or dirty/corroded. Disconnect them wire brush, then securely reinstall them & get the bolt tight enough so the connector cannot be moved or rotated at all by hand.
Battery replaced, same issue. How much water is copious amount? Took it to autozone to test the alternator, at first it started fine and showed no issues, then it came back low voltage, charge batter and retest. But the battery was at 100%. They want me to take the alt off the jeep and bring it in again so they can throw it in their machine to test... Opinions? Is the alt bad, even tho it will run the jeep without a battery once started? Do I have a short somewhere? Do I need to take out the alternator and clean it more? Any help is appreciated. 1999 TJ 4.0
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Old 08-14-2013, 04:09 PM   #15
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Originally Posted by Jerry Bransford View Post
Could be that your alternator is packed with mud, flush it out with copious amounts of hose water followed by copious amounts of WD-40 to chase the water out, or your battery connections are loose or dirty/corroded. Disconnect them wire brush, then securely reinstall them & get the bolt tight enough so the connector cannot be moved or rotated at all by hand.
Thank you! Put the hose on the alternator secured it, left it for 10 minutes, sprayed the hell out of it with WD40 and all is right with the world again :-)

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