Rough idle for about 2-3mins after start up. - Jeep Wrangler Forum
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Old 04-14-2010, 05:41 PM   #1
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Rough idle for about 2-3mins after start up.

Some times when I start my jeep it runs poorly for about 2-3 min. The jeep has no codes and I'm guessing it will probly be a sensor. Anyone have any knowledge on which one to check first. After the 2-3min it runs fine.

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Old 04-14-2010, 06:47 PM   #2
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Check the O2 first.

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Old 04-16-2010, 08:26 PM   #3
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The upper O2 sensor is your problem
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Old 04-16-2010, 09:35 PM   #4
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I'll check it out. Thanks for the input.
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Old 04-17-2010, 04:17 AM   #5
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During the first 2 or 3 minutes - up to 5, the O2 sensors aren't hot enough to give the ECM information. The ECM richens the mixture somewhat (a generic setting) to make it run smooth during that time. So it cannot be trouble with an O2 sensor.

But - check for a vacuum leak, hoses, TB base gasket, injector O rings, even the manifold gasket. Extra air is getting in somehow.

Get a "burnable" carb cleaner - dribble a few drops on the cement floor. If the puddle will burn, it'll work. Gumout works OK.
Spray it carefully on the suspected areas - listen for an RPM change. Don't forget to "go under" to spray on the bottom side of the intake manifold - use safety goggles, it can blind you.
Propane works even better.
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Old 04-20-2010, 07:48 PM   #6
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Maybe spark plugs? Mine does the same thing, but I have 45k on my stock plugs and am in dire need of a change.
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Old 04-20-2010, 11:13 PM   #7
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I found that I got some water where it wasn't supposed to be. Got the stuff dried up and gave it a tune up. Also sealed the drain in the bottom of my air box because thats how the water got in. I just know if I go up to my headlights to check the airbox for water. We stoped in a creek one time and without movement the water seeped in threw the drain wich is lower than the top of the head light which I use a guide of how deep I can go. Lucky for me it was just a very little and I didn't ruin my motor.
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Old 04-28-2010, 04:18 PM   #8
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Could you tell me where the water was? I have the same problem after doing some mudding.
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Old 04-28-2010, 07:17 PM   #9
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Could you tell me where the water was? I have the same problem after doing some mudding.
In the airbox/ into the motor.
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Old 04-28-2010, 07:18 PM   #10
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Wasn't alot but I got lucky. I know some people have issues with throtle possition sensors that tend to go out and make them run poorly. Not always water related.
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Old 04-28-2010, 10:16 PM   #11
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My 99 was doing the same thing but only for a minute or two after startup. I repositioned all the spark plug wires and checked the air filter for standing water. Messing with the spark plugs must have helped because the idle is smooth again.
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Old 04-29-2010, 12:05 AM   #12
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need more info. hot or cold start.could be many things.milage,service history.not 02. 02 only works in close loop.could be a coolant sensor.need more info.
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Old 04-29-2010, 01:45 AM   #13
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Could it be because of weak battery? I know my battery is almost dead because of winching and sometime it takes like a second to turn the engine over.

Rough idle goes away after about a minute if I rev the engine to about 2K RPMs (hot or cold engine). Seems like the battery gets enough juice after that to keep the engine running smooth.

What do you guys think?
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Old 05-18-2010, 06:05 PM   #14
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I'm facing a similar issue where it struggles slightly to start and will occasionally idle rough and shake the chassis for a minute or so. If it ends up being the battery then this will be my third Optima Red Top in less than a year.
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Old 05-18-2010, 08:04 PM   #15
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Just to let you know ... It wasn't my battery! It was one of the six spark plugs which wasn't gapped properly. Even though they were all supposed to be pre-gapped. As soon as I replaced it .. no more rough idle at all!
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Old 09-23-2011, 06:07 PM   #16
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This post seems helpful. I too am having a similar problem with my '97 Wrangler Sport. The Jeep starts fine, idles slightly rough, then for the first mile or two driving down the road, it seems to lose acceleration. I'll keep a steady amount of pressure on the gas pedal and the Jeep will speed up, then slow down, sounding like it's about to stall. At some times, there's a knocking sound that comes from the engine just as the acceleration comes back. Then after those first couple miles, it'll disappear and run just fine.

Per your suggestions I would like to check the O2 sensors. Is there a way to know if they're bad or not before purchasing the new ones? My check engine light is on, but it only gives me a Cylinder Misfire code. Nothing about a censor.
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Old 09-23-2011, 06:16 PM   #17
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Idle Air Control valve can also cause that the Idle to run low for the first few minutes. i just had to replace mine.
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Old 10-16-2011, 11:26 AM   #18
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Quote:
Originally Posted by Armstrong View Post
This post seems helpful. I too am having a similar problem with my '97 Wrangler Sport. The Jeep starts fine, idles slightly rough, then for the first mile or two driving down the road, it seems to lose acceleration. I'll keep a steady amount of pressure on the gas pedal and the Jeep will speed up, then slow down, sounding like it's about to stall. At some times, there's a knocking sound that comes from the engine just as the acceleration comes back. Then after those first couple miles, it'll disappear and run just fine.

Per your suggestions I would like to check the O2 sensors. Is there a way to know if they're bad or not before purchasing the new ones? My check engine light is on, but it only gives me a Cylinder Misfire code. Nothing about a censor.
I had the same code sometimes and it ended up being the upper 02 sensor. I had already replaced the lower so I knew it wasn't that. I replaced the upper and haven't had a problem since. Also the exuast always seems to work itself down from the manifold check that too.
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Old 09-25-2014, 06:19 PM   #19
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Rough first start

I had the rough start ups and engine light would come on a couple of times and found it was the purge valve kicking back emissions causing the engine to not run smoothly until a couple minutes passed. I have an 02 sport wrangler 6 inline AT

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