Another rough idle, and hesitation thread... I've done my research, and i'm stuck. - JeepForum.com

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post #1 of 22 Old 11-25-2015, 12:52 PM Thread Starter
jcurtis0520
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Another rough idle, and hesitation thread... I've done my research, and i'm stuck.

Hey y'all. I'm new to this forum, but not new to jeeps... I just purchased my 3rd jeep and I'm having a strange issue with it lately. I've spent hours researching forums on what it may be... but this one has me stuck, and i don't want to just throw parts at it trying to fix it...

Here is what is going on..
2003 Jeep Wrangler, 4.0L. Lately i've had a rough idle and the jeep will stumble if you bump the throttle, sometimes it won't recover and just die... It runs just fine through all other RPM ranges. The idle seems a bit low to me, between 450-500 rpm when hot. I don't have a check engine light, or any codes stored in the ECM.

Here is what i have checked so far.
-My cats are new, so we can pretty much rule those out as being a issue.
-the plugs have about 1000 miles on them.. they were put on in by the shop when they dropped a new motor in. They are champion RC12ECC plugs, properly gapped, which are what the emissions sticker recommended, but I've read that these newer ignition systems like the double platinum spark plugs so could the plugs i have now be causing this issue?
-All 4 oxygen sensors are fairly new
-I tested my TPS and it sits about .7 volts, and 3.7 volts at WOT.. Now here is where i am stuck. I've read so many places that your WOT voltage shouldn't be over 4.8 volts, or something to that effect... what i don't know is what is a acceptable minimum voltage for WOT? 3.7 volts seems low to me? Ive checked the sweep of the TPS and it seems pretty linear... no erratic voltages, or drops or anything...
-I've cleaned my IAC valve and throttle body, which didn't help any...

Any ideas? other then the rough idle, and stumbling issue the jeep runs fantastic. Thanks for all of your help.

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post #2 of 22 Old 11-25-2015, 02:43 PM
TheBoogieman
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Replace the IAC and get the battery checked (free).

I need some door surrounds. PM me if you know where I can get some used ones for a decent price.
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post #3 of 22 Old 11-28-2015, 10:41 PM Thread Starter
jcurtis0520
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Okay i replaced my IAC and it didn't change anything. My battery checked out fine as well... I also noticed the jeep only idles rough when the motor is at operating temp. Any ideas?
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post #4 of 22 Old 11-29-2015, 08:53 AM
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I've heard that changing the coil boots is a good idea. If you had the spark plugs changed they may have done that already.
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post #5 of 22 Old 11-29-2015, 09:17 AM
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If you manually hold the idle a little higher (800 rpm), does it run smoothly? In other words, do you have a low idle speed problem, a misfire problem, or both?

Did you disconnect the battery for about 10 minutes to reset the ecm so it'll learn the new iac more quickly?

Probably wouldn't hurt to run an injector cleaner in the tank and an intake cleaner.

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post #6 of 22 Old 11-29-2015, 02:05 PM Thread Starter
jcurtis0520
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Quote:
Originally Posted by bbacus View Post
I've heard that changing the coil boots is a good idea. If you had the spark plugs changed they may have done that already.
I havne't changed the coil boots, but i did take off the coil rail and inspect the boots, they seemed to be in good condition.

Quote:
Originally Posted by wadewen View Post
If you manually hold the idle a little higher (800 rpm), does it run smoothly? In other words, do you have a low idle speed problem, a misfire problem, or both?

Did you disconnect the battery for about 10 minutes to reset the ecm so it'll learn the new iac more quickly?

Probably wouldn't hurt to run an injector cleaner in the tank and an intake cleaner.
I've ran a couple bottles of injector cleaner through it over the last 2 months. No change. I've left the battery cable off overnight, no change either.

It doesn't really misfire, but it just sputters for a second or so when you bump the throttle, almost like it wants to die but it catches itself and then revs up smooth. If you hold the throttle at 1000 rpm or so and then floor it, it doesn't sputter as bad.

It only has issues when the motor is at operating temp. I plugged in a OBD2 reader and my idle speed is higher then i thought, 650 or so.. but its not consistent by any means.. it fluctuates and you can feel the engine vibrate...

With the reader i checked my TPS again by monitoring it with a real time graph.. its completely smooth throughout the throttle range.

It sounds like to me that maybe i have a O2 sensor problem... i know they are a Bosch sensor, which i've read our TJ's don't particularly like. So could that be causing the issues i'm having?
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post #7 of 22 Old 11-29-2015, 03:06 PM
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It can be a sensor like that. I know I've heard it several times on the forum. I've also had a personal one when we replaced the TPMS sensor in one of the tires on our WJ. The non-mopar version wouldn't work - had to replace it with mopar.

I would recommend giving the intake valves some cleaning by running some cleaner through the intake. Seafoam makes a spray for that, or you can feed it carefully through a vacuum line as long as it gets to all the cylinders reasonably evenly. I did it using the brake vacuum line on my TJ.

It does take some time for the ECM to learn a new IAC, but that should result in high or low idle versus what sounds like loping idle. Loping idle, to me, means IAC (which you've already done) or vacuum leak.

Here's the list from an FSM from a Honda. The principles are the same.

PossibleCause
. IAC valve mechanical malfunction
. Throttle body clogged port, improper adjustment
. Intake manifold gasket leakage
. Intake air hose loose/leakage
. Vacuum leak
. ECT sensor incorrect output
. Throttle Position sensor incorrect output

On one of the other threads that's live right now, the guy disconnected the first O2 sensor and the car ran great which verified the sensor issue.

Hope some of that helps.
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post #8 of 22 Old 12-05-2015, 09:02 AM Thread Starter
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So I replaced all 4 oxygen sensors with some NTK's. I left the negative battery terminal off all night to clear the adaptive memory in the ECM. Drove it to work this morning and it's running a little better but the idle when it's warm is still a little rough. Ive read I need to drive it more for the ECM to "learn" the new sensors and hope that it smooths out. Any other ideas as to what it could be?
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post #9 of 22 Old 12-05-2015, 09:41 AM
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I think that's exactly it. Drive it so the ECM learns the new components. If that doesn't come in line soon, don't forget trying a cleaner that goes in the tank for the injectors and combustion chamber and a cleaner for the intake to get the valves.

The other possibility that wasn't covered yet is that you could have a vacuum leak. One way to check for that is to spray starter fluid near anything that has vacuum (TB gasket, intake manifold gasket, vacuum lines, any ports on intake manifold, line to brake master cylinder...) If the rpm increases, whatever you just sprayed has a vacuum leak. When using this method, it's important not to get flammable starter fluid on hot things like the exhaust manifold

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post #10 of 22 Old 12-05-2015, 08:35 PM
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The fact that it only occurs when the engine is at operating temp indicates that the problem is most likely with the O2 sensors, which are not used in open loop mode when the engine is cold.


Also check the battery, battery cables, and grounds as a weak battery or corroded cables can cause weird issues.

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post #11 of 22 Old 12-06-2015, 11:04 AM Thread Starter
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Quote:
Originally Posted by wadewen View Post
I think that's exactly it. Drive it so the ECM learns the new components. If that doesn't come in line soon, don't forget trying a cleaner that goes in the tank for the injectors and combustion chamber and a cleaner for the intake to get the valves.

The other possibility that wasn't covered yet is that you could have a vacuum leak. One way to check for that is to spray starter fluid near anything that has vacuum (TB gasket, intake manifold gasket, vacuum lines, any ports on intake manifold, line to brake master cylinder...) If the rpm increases, whatever you just sprayed has a vacuum leak. When using this method, it's important not to get flammable starter fluid on hot things like the exhaust manifold
Ill re-check for vacuum leaks. I just replaced a few elbows and connections because they were leaking, but i might have missed something...

Quote:
Originally Posted by jkp View Post
The fact that it only occurs when the engine is at operating temp indicates that the problem is most likely with the O2 sensors, which are not used in open loop mode when the engine is cold.


Also check the battery, battery cables, and grounds as a weak battery or corroded cables can cause weird issues.
See thats exactly what i was thinking, which is why i replaced all 4 oxygen sensors. My grounds and battery cables are good, i cleaned those. I'm confused as to what i could be...

Here are some screenshots of the datastream of my TJ just prior to replacing my thermostat and oxygen sensors. (i replaced the t-stat because the temp would never get above 195. I bought a new thermostat from the dealer and filled the system with the correct coolant and now it runs at 210 like its supposed to) For those that are more familiar with the TJ operating parameters does anyone see any value that is abnormal?


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post #12 of 22 Old 12-06-2015, 11:39 AM Thread Starter
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Could it be possible my Camshaft position sensor is out of sync? I had a shop replace the motor and maybe they didn't install the sensor right?
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post #13 of 22 Old 12-06-2015, 02:43 PM
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Sounds silly - Gas Cap?

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post #14 of 22 Old 12-06-2015, 05:17 PM Thread Starter
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Quote:
Originally Posted by CrimsnTide View Post
Sounds silly - Gas Cap?
Checked the gas cap, its on tight, and seems like it seals good

The only other thing i can think of at this point is the coil rail is going bad? I also forgot to mention my engine ticks... i can't seem to track down where its coming from though.
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post #15 of 22 Old 12-06-2015, 06:12 PM
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Quote:
Originally Posted by jcurtis0520 View Post
For those that are more familiar with the TJ operating parameters does anyone see any value that is abnormal?

I am of no use here, however if you get oem parameters and compare to those it should highlight your problem.

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