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Rough Idle and Backfiring after warm up

5K views 11 replies 5 participants last post by  URascal 
#1 ·
My '98 TJ Sport has developed a backfiring issue and really rough idle after it warms up. This only lasts for a few minutes, then it runs fine to slightly high on the idle.

Any ideas on what could be causing this?
 
#4 ·
Problems like that which only occur after the engine has warmed up are normally caused by a bad upstream 02 sensor. The upstream 02 sensor is what the engine computer uses to set the air/fuel ratio after the engine has warmed up, it doesn't look at the 02 sensors when the engine is cold.

Your '98 only has one upstream 02 sensor instead of two like newer TJs have so you won't have to figure out which one is bad. Replace it only with an NGK or NTK 02 sensor, don't use Bosch which usually cause problems in TJs.
 
#5 ·
Problems like that which only occur after the engine has warmed up are normally caused by a bad upstream 02 sensor. The upstream 02 sensor is what the engine computer uses to set the air/fuel ratio after the engine has warmed up, it doesn't look at the 02 sensors when the engine is cold.

Your '98 only has one upstream 02 sensor instead of two like newer TJs have so you won't have to figure out which one is bad. Replace it only with an NGK or NTK 02 sensor, don't use Bosch which usually cause problems in TJs.

Thanks. I will give that a shot.
 
#12 · (Edited)
My 98 did the same thing. It would sputter and cough after one minute at startup and would continue for another couple of minutes. It ran fine after that until I turned it off and it did it again Replaced 2 O2 sensors, catalytic converter, no more problems. The catalytic converter was bad, it was rattling inside, so it needed to be replaced even though taking out the sensor would have destroyed it anyway.
 
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