Just got a 98 wrangler 4.0 Sport and its acting up. Previous owner reported that it needs to “warm up” or it will sputter and have issues. Only does it for a brief time and is sporadic... It acts like I’m hitting the accelerator quickly and then taking my foot off and repeats like that several times until returning to normal. Idle is a little rough as well. I ran theses issues and found articles suggesting it’s the TPS. I ran my scan tool and it pulled code P1391 which suggests an issue with the CPS. Looking for some advice about which one is the more likely issue.
P1391 code: Should I replace the CPS or TPS?
- Thread starter JeepersCreepers98
- Start date
If your code is for the CPS, than theres your issue. I would replace it with a mopar brand. TJs are picky when it comes to electrical sensors. Though it wouldnt hurt to clean out your IAC and throttle body it sounds like too.
On 97 models the code for a CPS sensor is the same code for a CAM sensor. It may be the same for your 98, though I am not 100% certain.
On 97 models the code for a CPS sensor is the same code for a CAM sensor. It may be the same for your 98, though I am not 100% certain.
Thanks for the quick response. I just wanted to verify that a CPS issue would create some of the issues I’m having. The check engine light was on initially when I bought it but then went away yesterday for no explainable reason. I pulled that code from the memory but the light is now off
X2 to this.
Make sure to use an OE Mopar brand replacement sensor or you'll have issues.
The issues you are describing can indeed be caused by the CPS going bad.
Also, if you do end up replacing the CAM sensor, make sure you are TDC of the compression stroke. I found that a plastic clothes hanger works well in cylinder 1, once it hits its highest point and you can feel the air being pushed out the cylinder, you know you are at TDC.
And X2 to @Chris . What you are experiencing is typical of a CPS/CAM sensor. When mine when south, it was misfiring badly and the tach was all over the place until it finally shit itself and the jeep would not start and left me on I25 at 1am in the morning waiting for a tow.
And X2 to @Chris . What you are experiencing is typical of a CPS/CAM sensor. When mine when south, it was misfiring badly and the tach was all over the place until it finally shit itself and the jeep would not start and left me on I25 at 1am in the morning waiting for a tow.
Thanks for the help guys, i ordered a Mopar CPS and hope to get it done this weekend. Will report back.
Does the problem occur whether the engine is cold or warmed up? A bad throttle position sensor can also cause a similar idle/acceleration problem. A bad idle/acceleration can be cause by lots of things including a bad TPS, O2 sensor (if the problem only occurs after the engine has warmed up), camshaft position sensor, or crankshaft position sensor. Worn out spark plugs too. 
Prior owner reports that it does it when the motor has not warmed up. I experienced it twice yesterday at 2
Different times... both the motor was around 100 degrees or so.
Different times... both the motor was around 100 degrees or so.
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