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Will you always get a code for a bad O2 sensor? 98 jeep wrangler TJ

Hi All,
I have been noticing in my TJ that when i start up in the morning, everything is fine. I then hit the road and about 30 seconds as I am accelerating the jeep starts balking and running rough, greatly losing power. I’ll push the clutch and watch the tach dip down to about stall, but I save it with a little gas. After about a minute of this power loss and stuttering, it seems to work perfectly fine for the rest of the drive. Once I park and let it sit off for a bit, it will do it all over again when I start on my way. I’m thinking bad O2 sensor, but not sure. I don’t have a check engine light or code to read, just performance. Any ideas?


It’s not your O2 sensor, you would get a code. You will need a mechanic to verify this, but I would look into the throttle position sensor (TPS). The TPS tells the computer that your foot is off the gas and the computer should control the idle through the idle air control (IAC). Sometimes the TPS gets dirty or worn down around the idle position so the computer never knows that it needs to take over. The computer does not detect an issue with this as it is simply not getting the correct voltage, but it usually gets some voltage.

It could also be a stuck IAC. The computer is sending signals to the IAC but it is not responding or not responding quick enough.

Thinking it without confirmation is guessing. Replacing parts on a guess can get expensive. Buy a code reader. Apps like Torque Pro ($5) can be installed on an android smart phone or tablet. A Bluetooth reader can be dad for $11 from Amazon. The readers are so cheap, there is no excuse for blind parts swapping.

A lazy O2 sensor may not set a code but there will be a small performance loss. Not what you are describing, though.

Edit: I like @keith’s suggestions!

Thanks fellas. But why does it run fine after it works through it? I agree on not blindly replacing parts.

Dirty or worn or sticking parts will act just that way. And act up at other times. Just how mechanical stuff works.

You have a throttle stop bolt on the Throttle body. It may be opening the throttle enough for it to idle while warm, but not cold.

These engine go into closed loop quickly, your oxygen sensor is slow and sending a rich signal causing the computer to lean the fuel mixture excessively and causing the engine to stumble. Replace the upstream oxygen sensor.

Ok, good stuff. Last update: temperature 35, I let it warm up seven minutes in the driveway, took my kids to school 2 miles away, ran smooth no problem. I then went to the hardware store, approximately 10 minutes inside, Start the jeep, pull out of the parking lot and as I accelerate to 25 mph heading to the grocery store a quarter-mile away is stutters it is low on power, right before I get there it clears up and runs perfectly fine.

You ever figure out what the trouble was here? My 97 is doing the same thing.