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Old 01-11-2017, 11:12 AM   #1
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Stumbling idle and flashing Check Engine Light

Sorry to the Moderator for posting in the wrong forum. This is where I thought I was posting.

Hi guys, I have a sputtering JK.
My 2010 has began acting up and since the dealer can’t get me in till Friday, I thought I would post up and see if any of you have got any ideas I can try in the meantime.
We have a 2010 Wrangler, 3.8 with an automatic.55,000 miles that has ran flawlessly till now.
Yesterday I stopped for a while and when I came back to start it, it wouldn’t start.Lights on the dash lit up but wouldn’t turn over.
So I had assumed the battery had died and pulled out my little Rockport jump box and jumped it and it fired right off…BUT…it was running really rough and I had the Check Engine Light, the ESP light, the Lightning Bolt (ie..ETC light) all on in my dash.
I cycled the key a number of times and all those lights went away but the Check Engine light remained lit.
Soon thereafter, the Check Engine light began blinking.I checked all the vital fluids and they were good so I limped it home.
When I put my code reader on it, it gave me the P0300 mulitiple misfire code.
I cleared the code and refired it and the code came back.
I check battery connections and they are clean and tight.
Checked battery voltage and it is 12.55v at rest
Checked the alternator output and it was 14.38v at idle
Since that initial no start with the battery, it’s fired off repeatedly with no issues.
When I first start it, the engine runs smooth but after approximately 10 seconds, it begins running rough and gives me a chime and the check engine light.
Since it runs smooth when I first start it I tend to believe it’s mechanically okay and realistically, the spark plugs, wires and coils are okay but something happens around 10 seconds in that trips the code and is making it run rough.
I will also add that when I was limping home, it seemed like it would “clear” itself out for a couple seconds and return to normal till it chimed again and then it would go back to a healthy stumble.
I checked all the obvious signs and nothing appears out of order.I read on numerous threads about how important a good battery is to these computers so I put my Battery Tender on the battery all night (after disconnecting the leads from the battery to totally eliminate any draw).
This morning I hooked everything back up and fired it off.It idled great for about 45 seconds before going back into the rough idle and flashing the Check Engine light.Given that that was a slight improvement, I decided to swap out the battery for a new one to eliminate the potential for a bad battery being a issue (and since I did get 7 years out of the original one as mentioned previously).
Put the new battery in and fired it off and sure enough, purred like a kitten till about 45 seconds and then the rough idle and Check Engine Light showed up.BUT, when I cycle the key to get the codes, it say “DONE” with no code.Yet, clearly something is wrong as the Check Engine light is flashing and it’s got a rough idle.
Any ideas?I have an appointment with the Dealer on Friday but if it’s something I can figure out, I sure would prefer that…
Thanks everyone……….john
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Old 01-11-2017, 02:31 PM   #2
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check your grounds and clean them up.

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Old 01-11-2017, 04:16 PM   #3
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Quote:
Originally Posted by nighowl2000 View Post
check your grounds and clean them up.
Okay, will do. I saw where they attach to a couple of studs on the passenger fender area and while clean (this is more of a mall cruiser than an offroad rig), there did seem to be a lot of the factory paint on the stud and nut.

Thanks for the tip...........john
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Old 01-11-2017, 05:57 PM   #4
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Well, the checked all the grounds and they were tight. I took them off anyhow and took a scotchbrite to the connectors and cleaned them up really well and then tightened them up again. Still does it.

It seems almost like the cold start injectors are carrying the load at the beginning as whenever you start it it fires right off and idles smoothly till a set period of time (around 40 seconds) and then it starts sputtering. It will set there and sputter till I shut it off. Then restart it and it idles smooth till about 40 seconds and then it does it again.
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Old 01-12-2017, 03:43 PM   #5
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hmm could be the TIPM fuel pump relay problem...

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Old 01-13-2017, 10:29 AM   #6
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Well, on the way to the dealer to have them look at it it started running really rough and the. Smoothed out to the point that I thought it had died till I realized that I was accererating. Sure enough, it's running perfectly now and purrs like a kitten. Pulled up to the dealer and did the quick key flash to see what codes and it says DONE. I'll let you all know what they find
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Old 01-13-2017, 05:27 PM   #7
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UPDATE: They couldn't find a thing wrong but suggested a Crank Position Sensor as a possibility but they sure weren't positive. So I brought it home and plugged my scanner in and it was still showing the P0300 code. I erased it and it went away and it seems to be running great.

Not sure what to think (other than the dealer was of zero help, other than taking $130 from me)
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Old 01-13-2017, 10:59 PM   #8
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I dont know why everybody immediately assumes a ground. This isnt 1970.

P0300 is a random cylinder misfire. All of my experience with this same issue comes from the 3.6 so I cant be 100% sure. A CPS can definitely cause this. It's a cheap part and anybody with 2 hands can change it out.

If anything, wait till it does it again and see if you can get more codes. I got an intermittent CPS signal code when I had a wiring problem to my CPS.



I have tons of codes, so ignore a lot of those. That's just page 1 of 3. A lot of them are due to the deleted emissions system and goofy ABS.
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Old 01-14-2017, 02:20 PM   #9
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Well, I drove it over 100 miles today and it ran flawlessly. Who knows.... I'm going to give it some love and put some new plugs, filters and fluids but at the moment, it's back to normal. I can't help but think that the battery was the issue given it started with a dead battery.....
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Old 03-07-2017, 09:30 PM   #10
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Hello, how has your jeep been running? I have almost the exact same problem I am working through on my jeep that all started when I had a supercharger installed. I had my battery checked and it "passed".

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