rough idle at stop with engine warm

[southernwake]

Started today. Made a 6 hour round trip and on the way home I noticed when I came to a complete stop ( stop light/ stop sign) the idle would be erratic. It was on the low side and felt like it was fighting to stay running. About a block away from the house it did it and it almost died, I hit the gas and it revved up. Got in the driveway and stopped and she shut off. Put it in gear and fired her back up, she fired up like normal and held normal idle.

I am getting no CEL. About 2 months ago I removed the IAC and cleaned it. Plugs/coils have 19k on them. Trans drained and filter replaced about 7k ago. I did some research and one guy had a trans filter pop off and that was causing his issue (?). I saw everything from that to IAC, bad coils, fuel pump etc With no CEL and it only happening in gear (assuming this since she fired right back up in park after stalling in gear) I am not 100% sure where to start on this. Any ideas??

I should also add that under acceleration there is
No bogging down. Getting pretty good gas mileage, actually seeing an increase here recently. Only thing I did today was charge the AC, add some Lucas fuel treatment 1/2 through trip and topped off oil.

 

[HoosierJeeper]

Is the throttle body clean?

I had a horribly rough idle in the LR3 that I thought was a MAF sensor (although the KJ has a MAP sensor), replaced that several times, did the fuel treatment stuff and finally cleaned the throttle body for the hell of it and it was like night and day. Felt new. It was horrible before. It would surge from about 200 RPM to 900 RPM constantly. I got a CEL for the MAF sensor a few times but even with that resolved it never idled smooth.

 

[ltd02]

I'd do like HJ said first. Just a note, when my TPS was going it would do that off and on until it finally threw a code.

 

[Damotee]

Only thing I did today was charge the AC, add some Lucas fuel treatment 1/2 through trip and topped off oil.

The fuel treatment could be the culprit. It might have cleaned off a bit of sludge from the injectors and the stuttering is the result as it gets burned off.

 

[southernwake]

HJ, it has 137k on it and I havent cleaned it since I have had the last 19k, so I am going to guess it has never been cleaned. I will take that off tomorrow afternoon and get that cleaned up and see if that helps. I figured it was probably something along those lines or a possible bad IAC/TPS.

 

[southernwake]

I was curious if maybe the fuel treatment may have had something to do with it. Since it wasn't doing it when I had it idling for charging the AC.

Update: after letting it sit for a few hours I went out and started it. Temp gauge was showing it was at the 1/4 mark for engine coolant temp. The idle was rough, but not surging/ hunting like it was when i was sitting at a stop light.
I pressed the gas pedal and it didn't stutter, it revved up smoothly. Definitely at idle has an issue. Still no codes. I am going to drive it to work tomorrow morning ( 10 miles). I will be taking the throttle body off and cleaning it when get home. Unless for some reason anyone thinks it shouldn't be driven.

 

[LibertyTC]

The IAC has a lot to do with idle as well, so clean the IAC and the port well too.
In post # 10 I have some good photos, shows how dirty things can get in there....
Link: http://www.jeepkj.com/forum/f196/idle-air-control-no-screws-44826/

 

[southernwake]

I cleaned the IAC a couple months ago. I sprayed the IAC with carb cleaner and cleaner it off really well. I then sprayed a rag with carb cleaner and wiped out the port as well as I could. I let everything dry and when I fried her up she ran a little higher rpm for about a minute and then she calmed down.

Fired it up this morning and she idled like normal with a cold motor. Drove to work ( about a 12-15 minute drive) and she was nice and warm. Pulled into a parking spot and sat there in gear for a few seconds and she idled like normal.

So this afternoon I am going to take the throttle body off and clean it out and remove the IAC and replace it. Now I know you can remove the IAC w/o removing the throttle body, but I used a cheap torx bit and it of course broke off in the screw head on the lower screw when I reinstalled it last time. So... I have that going for me too. :emotions34:

 

[HoosierJeeper]

I have a stripped torx head on the TPS lol. Fun times.

 

[LibertyTC]

Ya they can be on tight..this is my set up...
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I tape the bit to ensure it wont fall off, and no movement when breaking it loose. :gr_grin:

 

[southernwake]

I cleaned the throttle body yesterday afternoon. It was in need of a cleaning but wasnt the worst I have seen. I also just replaced the IAC with a new one.

I did fine that one hose coming from the air box that sits on the throttle body, on the passenger side I had a hose that ran to the back of the passenger valve cover and connected there. That hose popped off when I was was removing the box and I noticed it has a split in it on the valve cover side.

Once I was done with everything I fired her up and she started and then idle crept up and was in the 3k range for about 20 seconds and then slowly fell. The brake pedal was super hard at this point too. I missed the brake booster line that hooks into the intake. Brakes worked a lot better once I reconnected that. Drover her around town and to work this morning and no idle issues at this point. Will continue to monitor and see how she does. Thanks for the suggestions

 

[larryblevins]

My 2012 Jeep liberty also starting skip missing while at idle or cruising in the 1500 rpm. It has 100000 miles on it and 30000 miles on the spark plugs. I changed the NGK G power plugs and installed double platinum autolite plugs and new spark plug wires. I also cleaned the air flow sensor with electrical contact cleaner. I did notice that their was a residue built up in the throttle body inlet around the throttle body valve. I sprayed it with throttle body residue and wiped it out with a clean rag. It appeared to be oil / dust base. My jeep is knowing running as good as new. 50 miles at all speeds and no more missing. I was ready for spark plugs and wires but I think the real issue was the dirty throttle valve.