[titansfk]

98 TJ 6cyl 5sp

I have this strange hesitation problem that developed about one month ago.

When the engine is cold (any time of year) I drive for about one minute and then it starts to buck. It sputters at any throttle possition other than idle or WOT. I usually go WOT for 15 sec and then it will run perfectly for the entire time I drive. If I let it sit for a 8 hours (while at work) it will do the same hesitation problem.

I sprayed carb cleaner in the carb, and replaced the throttle position sensor, but it still has the problem.

Anyone had this problem, or have any ideas?

Thanks.

[Jerky bump]

Any chance you got water in your fuel?
It almost sounds like it runs okay after "warm-up". Have you let it sit idling until it warmed up and then drove it?
There is a boat-load of causes for poor engine performance. Hope someone can help you.

[titansfk]

I will let it idle tonight before I drive home. This should tell me if it is temperture related.
Good idea, thanks.

[Sweeney]

The carb might be the problem... it's not suppose to be there.

[titansfk]

I bet that is the problem. I ripped it and and put the throttle body back in.

Yes I meant throttle body, not carb.

[Jonny Jeep]

Upstream O2 sensor. I'd bet on it!

Mine acted exactly the same way when it went bad. It didn't throw a code either. Try unplugging the sensor and see how it runs. It should throw a code after it's unplugged but you will probably find it runs OK. The sensor is in the exhaust pipe just below where it joins the exhaust mainifold. The plug is clipped up at the rear of the inlet manifold. Should run you about $50 from most places.

[titansfk]

I forgot to mention that it did throw me a O2 sensor code, but I tested the sensor(s) resistance and voltage and they checked out. I reset the computer and it never gave a check engine code again, but the problem is still there.
Since this was the cause of your problem, I might just change it for the hell of it.
Thanks.

[Jonny Jeep]

Try unplugging it and it should drive fine which will confirm the O2 sensor is faulty.

[titansfk]

I disconnected the upstream O2 and it seems to work. After about 5min the check engine light came on. Tomorrow morning will be the true test. If it works I will replace the sensor.
Thanks. You guys are fantastic.

[drbobt]

Sorry to bring back an old thread but my 98 Sahara 4L Auto just developed the same symptoms as the OP. I tried disconnecting the upstream O2 sensor but unfortunetly this did not help. Problem seems to go away also if I let it idle for about 5 to 10 mins. Any additional thoughts would be appreciated. Also was wondering if the OP problem was fixed by replacing the O2 sensor.

Thanks