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Rough Idle, Bogging down from stop

16K views 45 replies 11 participants last post by  manderson2228 
#1 ·
I bought a 2004 wrangler back in august and have had an issue with this since i bought it. At a stop light and not every time, the jeep will idle low, and act like it's going to stall, when i get on the gas to move it will for a split second DROP quickly in RPM and bog down then take off. I've had it stall a few times. While it's running rough at the stop lights, if i put it into drive it smooths out and runs fine, but back in drive it runs rough. I've done everything I can think of to fix this, but I am at a loss at this point. Let me tell you what i've done/replaced

TPS Sensor (mopar)
CPS Sensor (mopar)
MAP Sensor (mopar)
Cleaned IAC
Had the throttle bottle cleaned
New Fuel pump
New plugs (autolite)
New O2 Sensors all 4 (ntk)
Ran some BG fuel system cleaner through

Any help is really appreciated.
 
#5 ·
I bought a 2004 wrangler back in august and have had an issue with this since i bought it. At a stop light and not every time, the jeep will idle low, and act like it's going to stall, when i get on the gas to move it will for a split second DROP quickly in RPM and bog down then take off. I've had it stall a few times. While it's running rough at the stop lights, if i put it into drive it smooths out and runs fine, but back in drive it runs rough. I've done everything I can think of to fix this, but I am at a loss at this point. Let me tell you what i've done/replaced TPS Sensor (mopar) CPS Sensor (mopar) MAP Sensor (mopar) Cleaned IAC Had the throttle bottle cleaned New Fuel pump New plugs (autolite) New O2 Sensors all 4 (ntk) Ran some BG fuel system cleaner through Any help is really appreciated.
I have the same problem. I was told to clean the throttle body. Will let you know how it works.
 
#6 ·
Question about the vacuum lines, is there a better upgrade for them? I am have the same problem as the original poster. I noticed recently that the two elbows next to the green cap in your picture ( tester cap ), keeps vibrating loose on mine from offroading and hitting bumps. Then my jeep does the same. rough idle and loses power. I was thinking it is the Oxygen sensor for the upstream since mine is gone.
 
#7 ·
So i already cleaned the throttle body. Actually had the shop do that one.

I went out and checked the elbows, they look ok to me, short of some gunk inside when i pulled them off. I am probably going to buy 4 new ones anyways because they are so cheap and just put them on.
 
#8 ·
No need to replace them unless cracked, dry or loose.
Mine were OK (not lose), but "dry" and rubbing off black on my fingers.
I am just going through this TJ and replacing anything questionable.

The Doorman 766330 is $5.99 each at O'Reilly.

On the purge canister, they are a perfect 5/16 x 5/16. However the OEM has two molded together and the two Doormans will need to be shaved on the sides to match the center distance of the purge canister ports.

On the front intake manifold port, it requires a hose clamp to secure over the 1/4 port.
On the middle intake manifold port, I used a hose clamp to reduce the possibilities of cracking from expansion over the 3/8 port.

The rear elbow is factory. I have an Edelmann 76630 on order from O'Reillys for $2.99 ($1.99 at Summit Racing)

manderson2228, it does not seem that a vacuum leak at the intake manifold is your issue.
However, I would check manifold vacuum before putting more $ into parts.
 
#9 ·
This doesn't sound like a vacuum related issue. My bet is either the TPS (throttle position sensor) has gone bad, which can cause an erratic throttle response, or the throttle body cleaning process was not thorough enough to also clean the IAC (idle air controller) which is what provides the engine with all of its air at idle RPMs when you're not stepping down on the gas pedal.

The IAC can be removed and cleaned, you only need an aerosol can of throttle body cleaner and a toothbrush to clean its plunger, and a baby bottle nipple brush to clean the orifice in the throttle body the IAC's plunger fits into.

SOMETIMES it can be cleaned without removing it by spraying the throttle body cleaner into the throttle body while the engine is running and the engine at idle RPMs. The IAC will suck the cleaner in through itself but only when the RPMs are at idle. The engine will likely stall repeatedly when you spray at idle RPMs but that's ok, that's just a sign the IAC is sucking the cleaner in through itself. Just restart the engine when that happens.

The IAC can simply be cleaned to restore it back to operation which only costs the amount of a can of throttle body cleaner. The TPS cannot be cleaned, it has to be replaced when it goes bad. So clean the IAC first and if that doesn't do it, replace the TPS with a Mopar OEM replacement from the dealer. Never trust aftermarket sensors, the majority are cheap imports.
 

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#13 ·
I've been having similar problem, I replaced several things (map sensor twice) checked grounds and voltage. The trouble would come and go, hot or cold, wet or dry, sometimes when it was running for hours with no trouble, sometimes it had only been running for miniutes. Finally found the trouble and it cost nothing to fix... it was just a dirty connector going to my Super chip, cleaned it and havent had any trouble since. Hope its as easy as that!!
 
#14 ·
I checked all the connections going to the computer and everything nothing obvious. I filled up two days ago and after using some of the BG fuel system treatment in the gas it does seem to be running better. Although it will still low idle every once in awhile at a stop light. Interestingly I also noticed today that if it is idling low, if i shift into neutral it goes back to normal. If I shift into neutral and then back into drive, it will also go back to normal. I should mention I have an automatic. Hopefully this new info might help someone. Maybe something with the transmission?
 
#18 ·
I've had it happen both when warm, and cold. The last time it stalled I was barely out of my neighborhood and not up to temp yet.

On Saturday for example it was doing it when warm, out of maybe 20 or so stoplights it ran fine at 17 of them, and the other 3 real rough. Quick shift into neutral, and back into drive again, and it leveled out.
 
#16 ·
9 times out of 10 a low idle on modern day engines, particularly so with speed density systems, is caused by IAC/dirty T-body issues. Just because your IAC is clean does not me it is working correctly on the electrical side of it. If you have access to a scan tool with Jeep software you can control the IAC and see if it meets the requested RPMs. If you do not I would suggest to replace the IAC and recheck.
 
#17 ·
I just fixed my jeep issue doing this, well temporarily fixed it. My O2 sensors are gone, so for now I unplugged the upstream sensor until I buy a new one. The jeep has been running very good. I also had to fix those vacuum line elbows that were vibrating loose. Took the jeep wheeling twice, and shes running as good as new again! good luck with yours
 
#21 ·
I am not familiar with that scan tool but their website claims to have bi-directional controls so maybe, but typically the lower end scan tools don't do manufacture specific tests. Have a look around when it is connected, Usually it would not be in the generic OBD II part of the scan tool. If there is a way to communicate with the ECM by inputting the make, model, and, year of your jeep, or VIN entry do that and look for any tests you might be able to perform.
 
#26 ·
Some problems can be diagnosed over the internet easier than others. It is hard to say what is going on based on description alone, one person low idle description is another persons misfire description and so on.

You have a diagnostic tool how about we put it to use. Plug in your innova 3140 and see if any codes are stored. Then while the problem is happening look at the live scan data. What I would like to know about is the long and short term fuel trims (STFT & LTFT B1/B2), Map sensor, ECT, and O2 sensor data. With this data I may be able to point you in a direction, ideally you'll be able to get this info to me graphed over time.

Can this scan tool upload a report of the live data to your computer that you can upload here? If so please do so, if not try and describe what data is doing or take a picture or video of the scan tool screen.
 
#29 ·
If it can be graphed and uploaded include the fuel trims, O2 sensor, Map, Calc load, and RPM's. Get the engine to operating temperature and get 10-15 seconds of the engine idling, 10-15 seconds of steady cruise (keep gas pedal steady at 45 mph or so), and a hard acceleration from a stop up to freeway speeds with the pedal floored.
 
#30 ·
So i've been driving around with the damn computer in the vehicle. Long story short it hasn't done it again. I believe replacing the IAC might of done it. It did it once, slightly different the night i swapped it, but i think the sensors might of needed to adjust themselves as i didn't reset the ECM when I replaced the IAC.
 
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