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Old 06-03-2013, 02:28 PM   #1
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Throttle Hesitation

My 98TJ 4.0 will jump and buck at a certain point in the throttle. Its early in acceleration when this happens. If u hold it in 2nd gear at about 30 it will buck and jump until i either let off the gas or press it harder. It doesnt do this at any other point of acceleration. The engine runs, shifts, accelerates, decellerates, and will idle perfectly. There are no mods to programming. Only mod is a throttle body spacer. So....what could it be?

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Old 06-07-2013, 10:45 AM   #2
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No response...great!

Now i replaced the TPS after talking to a local mechanic.....No change. It seems to happen at the 2000 rpm range exactly regardless of the gear. If i hold the throttle there it jumps and misses and it even backfired through the intake once yesterday...all after replacing the TPS. I dont underatand...what the hell would make it do that at a certain rpm?.

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Old 06-07-2013, 10:54 AM   #3
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This happens during a cold engine or warm or all the time? Remove spacer and see if it still does it.
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Old 06-07-2013, 11:37 AM   #4
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It does it all the thime everytime. Cold hot doesnt matter or make it any better or worse. It reminds me of a misfire like its sputtering..i cant discern if its electrical or fuel....but my thinking is if it only does it at a certain rpm it must be electrical...but ive been wrong before.
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Old 06-07-2013, 12:19 PM   #5
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Have you checked plugs and cap? Bad wire?
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Old 06-07-2013, 12:32 PM   #6
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I havent since it was only happening at the 2k rpm range i wasn't thinking they couldnt be failing. But like i said before "i have been wrong before".....they are rather new also but it sounds like thats what i should replace next huh?
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Old 06-07-2013, 12:50 PM   #7
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Check your cap and pull plugs. It's possible that one is off, you are getting gas to the cylinder but the plug is not firing properly causing you to bog and slightly flood that cylinder for a moment. I'm not sure. Could also be a wire. Our suppression cables are not as reliable as the solid core wires and just kinking them can cause issues. The good thing about the suppression cables is that you don't hear the sound interference in your stereo
I have had the issue before and once I got going, all was fine.
if it was my jeep, I would start by checking plugs and cap. We only ha e a few plugs..
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Old 06-07-2013, 12:58 PM   #8
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Small list of things... in the order I would try
CPS
Plugs
Ignition coil
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Old 06-07-2013, 01:01 PM   #9
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Thanks guys...i will knock these out over the weekend and report back. I have a new CPS left over from my 97 XJ it would most likely work on the wrangler wouldnt it?
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Old 06-07-2013, 01:08 PM   #10
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There are two CPS, try the crank first. Not sure as to your question.
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Old 06-07-2013, 01:46 PM   #11
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First, I'd remove that TB spacer which does literally nothing when placed under the air-only type of throttle body the TJ uses. Spacers can perform magic when placed under carburetors or older TBI (throttle body injection) throttle bodies that pass air-fuel mixtures through them, but not under the TJ throttle body that only has air passing through it. The TJ's fuel is injected directly into the combustion chambers well below the throttle body.

Erratic throttle response can be from a lot of things but the first things I'd do/check are this... with the engine running, clean the throttle body's interior with an aerosol throttle body cleaner. If that doesn't cure it, remove the IAC (idle air controller) from the throttle body & clean its plunger & the oriface in the TB the plunger fits into. Then I'd next suspect the TPS (throttle position sensor) also mounted on the throttle body. The TPS cannot be cleaned, it can only be replaced. I actually suspect the TPS is the cause of your issue but the other suggestions I first suggested are a lot less costly to try first & it's always a good idea to clean the TB's interior & IAC.

Finally, if none of that helps, it is likely a bad upstream 02 sensor. I wouldn't suspect either of the CPS's (crankshaft or camshaft position sensors) at this point.
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Old 06-07-2013, 02:13 PM   #12
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Jerry could be correct, especially if u just added the throttle body. Good call. Check all the free stuff first!!! Sucks to trouble shoot
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Old 06-07-2013, 02:16 PM   #13
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Quote:
Originally Posted by Jerry Bransford View Post
I actually suspect the TPS is the cause of your issue but the other suggestions I first suggested are a lot less costly to try first & it's always a good idea to clean the TB's interior & IAC.

He already replaced this part, buried within a later post. What would you do next?

I had this same issue on a dodge neon that I ran in LeMons. It was a serious PAIN IN THE F****** ASS to fix. Blip/hesitation at 3k rpm and full on disaster at 5k + I don't even know what fixed it specifically as we replaced just about everything.
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Old 06-08-2013, 10:13 AM   #14
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my buddy had the same problem replaced the TPS wasnt that the clock spring went in it but we did find out that on the 97-99 there is a recall on the clock spring so might want to look into that
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Old 06-08-2013, 10:33 AM   #15
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Quote:
Originally Posted by RedTJ00 View Post
my buddy had the same problem replaced the TPS wasnt that the clock spring went in it but we did find out that on the 97-99 there is a recall on the clock spring so might want to look into that
What Recall? I know of no recall for the clockspring on '97-99 TJs.
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Old 06-08-2013, 04:46 PM   #16
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Could it be the PCM? I think it was the TCM in models earlier than '06. There is a three-page PCM thread on this forum.

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