• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

rough idle

I doubt it. What I have read here is the ECU monitors the battery temp to prevent overcharging the battery.
 
check engine went away on the way home. I agree with hypoid i dont think this is correlated.
the engine continues to run fine and this new issues came and went first time ever today. bad fuel still seems more probable.
 
4x4JeePmaNthINg said:
Check engine liget came on today and the code is for the battery temp sensor. Could this be a culprit rather than bad gas?
Click to expand...

If the sensor is defective or the wire to it damaged, then it is not related. If the battery indeed got too hot, it could have plates shorting out internally, and that can come and go until it opens to zero volts, DOA, or a cell shorts out and the max voltage drops to about 10 Volts, and the battery would over heat while charging due to the short. Seen two lead acid batteries explode in life time from shorts. Last one I caught it over heating and not taking the charge, shorted plate and one before that died to 0.00 volts, disconnected completely internally, meltdown of some sort or busted post....

If the battery voltage was jumping temporarily due to a short that burned out for now, yes it cause a rough idle, but bad batteries usually show up as low voltage on the dash gauge and or no crank situations.
 
4x4JeePmaNthINg said:
the battery is very new, Interstate. I replaced it when my alt died because a few weeks later the battery lost too many cranking amps.
Click to expand...

Then I would stop by the place you bought them and have them use a tester on the running rig, and test the battery and starter for capacity and load.

New batteries can go bad. Never write off any new part as not being a possible source of a problem. Did the battery temp sensor get damaged in the swap and/or reconnected (the recent CEL code)?

Also, the newer rigs seem to have the voltage regulators in the ECU or PCM, instead of the alternator. One more reason I like the old Renix rigs, you got new ones with the new alternator, without getting hosed for PCM.
 
I checked the sensor and its plug which all seemed fine. I can get the battery/ starter tested however if ive never experienced these symptom pre/post occurence would you still think i should get these items tested? I havent had a hickup since.
 
4x4JeePmaNthINg said:
I checked the sensor and its plug which all seemed fine. I can get the battery/ starter tested however if ive never experienced these symptom pre/post occurence would you still think i should get these items tested? I havent had a hickup since.
Click to expand...

That's up to you, depends on how anal your are LOL. I have my own volt meter and test my own for my own piece of mind....when needed. But I would watch for any events that come up and keep those on your possible cause or related items list...

Something caused the idle issue and something threw the battery hot code.
 
Ecomike said:
Then I would stop by the place you bought them and have them use a tester on the running rig, and test the battery and starter for capacity and load.

I have a multi meter but what is ment by checking for load and capacity? also why am i checking the starter?
Click to expand...
 
Last edited:
Drove to work again and sat idling for 10 minutes. It didnt idle as bad as the first time but would dip a hair lower than 750 then bump a hair over then normal for a while until repeat.
 
4x4JeePmaNthINg said:
Ecomike said:
Then I would stop by the place you bought them and have them use a tester on the running rig, and test the battery and starter for capacity and load.

I have a multi meter but what is ment by checking for load and capacity? also why am i checking the starter?
Click to expand...

Bad alternators can damage a battery, and a bad battery can damage a starter or an alternator, or voltage regulator (Old rigs it was in the alternator, new models it is in the PCM computer)..and a bad starter can damage a battery. By bad starter I mean one that is partly shorted internally pulling too much current, but still seems to be working with a fresh battery.

With a volt meter you have some one crank the engine, while you monitor the battery post to post voltage. If it drops under 10 Volts while cranking, something is wrong. BY testing the voltage you are testing the coupled battery-starter system. If the voltage drops below 10 volts, it does not tell you which part is bad. The stores can load test the battery by itself with a resistor pile in their tester to see which is the problem.

Your first thoughts on a vacuum issue may be right, it could also be a marginal O2 sensor system, where the sensor gets too cold at idle and switches to open loop, that could be a blown fuse, damaged sensor wire (they damaged easily due to their locations), bad relay on the older XJs, or bad heater in the O2 sensor. That too can be tested with a volt-ohm multimeter. The dip in idle and recovery is from the PCM switching from closed loop to open loop mode.

The PCM changes the IAC (Idle Air Controller) setting-air feed rate to manage the air to fuel ratio in response to the O2 sensor data. So if the IAC is not sticking, id look at testing the O2 sensor system, wiring, fuse, and sensor..

Here is a how to thread on O2 sensor testing

http://www.naxja.org/forum/showthread.php?t=1012701&highlight=oxygen+sensor+test
Click to expand...
 
both upstream and downstream O2 sensors are bosch and less than 3yrs old. for whatever reason this issue is only after a good drive then sitting idling for a while. the only other issues since are the battery temp sensor code that went away same day.

Ill continue to inspect your recommendations and update whats going on.

If it is vacuum how can i test the lines? tried smoke but saw nothing- probably not the best test. Ill pull the TB this weekend and clean IAC/ inspect tps.
 
Last edited:
You can test wiring and vac hoses by moving them at times when it would usually act up to see if you trigger the speed change. You can also spray carburetor cleaner aerosol at vac hose connections and intake gasket locations to see if the rpms change.

Have you tested the fuel pressure? It sounds like a heat sensitive trigger, like heat soak in the fuel line/injectors, or a sticking injector. They can be tested using a hair dryer to heat up parts and see if they are heat sensitive, like a CPS or spark coil. It is really hard to find a failing part till it fails for good. I have your problem off and on for years on various rigs, and never really found the source, it was more like a combination of marginal issues, age related.....But one by one as I fixed things, it went away once everything was mostly new and clean and well sealed.
You might clean out the CCV line with the orifice in the rear. They get trashy at times. I had a loose injector connection on one that took me years to run into.

4x4JeePmaNthINg said:
both upstream and downstream O2 sensors are bosch and less than 3yrs old. for whatever reason this issue is only after a good drive then sitting idling for a while. the only other issues since are the battery temp sensor code that went away same day.

Ill continue to inspect your recommendations and update whats going on.

If it is vacuum how can i test the lines? tried smoke but saw nothing- probably not the best test. Ill pull the TB this weekend and clean IAC/ inspect tps.
Click to expand...
 
I haven't tested fuel pressure since I upgraded the injectors a couple years ago. She fires up instantly so I don't think it's pressure related. I think it was 49psi at the rail with very slow bleed down after turned offrom, never below 35.
 
4x4JeePmaNthINg said:
I haven't tested fuel pressure since I upgraded the injectors a couple years ago. She fires up instantly so I don't think it's pressure related. I think it was 49psi at the rail with very slow bleed down after turned offrom, never below 35.
Click to expand...

The 49 psi fuel pressure is needed to keep fuel from turning to vapor and vapor locking the engine on a restart when there is heat soak, caused by sitting there hot with no air flow, off or at idle.

My thought was it might be getting just close to the edge of vapor lock. You could test the idea by shutting jeep off after a long idel just as it hick ups, then wait 3-4 minutes then restart. If it does not start or idles worse, check the fuel pressure at that time.
 
Ecomike said:
That sounds more like a heat soak and or fuel pressure leak down issue after the pump/engine is turned off problem to me.

So today i got to work early and i let the car run while i listened to the stereo. I got the same symptoms of rough idling like a consistent misfire after 15-20 minutes of sitting idling. I have brown dog motor mounts/ straight pipe so when this happens its very noticeable.

After peeking around in the engine bay i have found my second from the grill cylinder/ exhaust manifold tube has a large crack. My theory is that at idle the heat is building through the intake and causing the previously mentioned heat soak. the crack is maybe like an inch+ on the out side of the exhaust tube.

what say you, good bet?

also this is not my stock manifold and is an oem replacement with the accordion looking flex areas, off topic, but im open to new replacement recommendations.
Click to expand...
 
My Ford F250 had the same symptoms as your XJ. Rough idle, rough running. Not always consistent. CEL light did not come on. But I pulled the codes with the key on-off trick, and it indicated a bad MAP sensor.

I replaced the Map sensor, and problem solved. Ran smooth as butter again.

Don't know if this is your problem or not, but you should try pulling codes and/or testing your MAP sensor. Not all codes light the CEL.
 
You must log in or register to reply here.

Similar threads

I
High idle, smells like gas, running out of things to replace
Replies
2
Views
2K
Inverhyt
I
I
2000 Cherokee XJ Misfire Mystery
Replies
12
Views
213
Tim_MN
Tim_MN
A
Rough idle & CEL with no codes?
Replies
10
Views
3K
alopeks
A
O
2000 XJ Failed Colorado Emissions high CO
2
Replies
27
Views
2K
Ken M
K
Z
1990 renix electrical issues
Replies
3
Views
92
cruiser54
C
Back
Top