engine hesitation runs rough until operating temp

manion · 09-02-2008, 06:42 PM

I have a 99 tj 4.0 engine runs rough or cuts out until it warms to operating temp. It actually does this worse if you drive it some where let it sit for about 20 minutes or so then go and drive it, it cuts out hesitates like there is no throttle unless you floor it, then once it warms to operating temp it runs ok. There is no check engine light, I have changed all plugs wires rotor bug and dist. cap I checked fuel psi it was 48 psi and held psi more than 30 psi after the engine was shut off, some one told me it might be the eps so I changed that no help any ideas would be apprieciated. Also every time it rains or I wash it it gets water in the floor board is there a drain some where for the vent?

manion · 09-18-2008, 09:15 PM

bump bump bump

Mattbastard · 09-19-2008, 10:47 AM

My old S-10 did this. Coolant temp sensor made the ECM think it was always up to operating temperature.

Is it backfiring through the intake when cold at times? This is a possibility.

letsgomuddin · 09-19-2008, 11:01 AM

Mine did this also, it seemed worse in the winter too. It was my oxygen sensors. If your jeep has over 40K on it, and you haven't changed them, start there. Also a bad temp sensor will cause this too, but keep in mind that there are two temp sensors on your TJ! One is at the thermostat housing and that runs the gauge only. The other is toward the back of the engine on the driver's side.

bigj1974 · 09-19-2008, 11:09 AM

Quote:

Originally Posted by manion

I have a 99 tj 4.0 engine runs rough or cuts out until it warms to operating temp. It actually does this worse if you drive it some where let it sit for about 20 minutes or so then go and drive it, it cuts out hesitates like there is no throttle unless you floor it, then once it warms to operating temp it runs ok. There is no check engine light, I have changed all plugs wires rotor bug and dist. cap I checked fuel psi it was 48 psi and held psi more than 30 psi after the engine was shut off, some one told me it might be the eps so I changed that no help any ideas would be apprieciated. Also every time it rains or I wash it it gets water in the floor board is there a drain some where for the vent?

cleaned out the idle air controller?

manion · 09-19-2008, 02:22 PM

yes since this post I have cleaned the throttle body and cleaned the IAC also have changed the tps thought that the tps fixed it as it didnt do this for a couple of times but it is still there doing same thing.

**Zew** · 09-19-2008, 03:06 PM

I have this same problem and the only thing i didn't change out was the engine coolant sensor. I think that's gonna be my next try. I changed the O2's, tried 3 different sets of spark plugs, 2 cap and rotor sets, 2 sets of wires, TPS, CPS, CamPS, replaced the coil and Cleaned the IAC and TB. Nothing helped.

angryjohnny · 09-19-2008, 03:27 PM

I had the same exact problem I disconnected the front bank o2 sensor it runs like a champ now it throws a code I know this is a temp fix for it i havent figured it out yet but i do know my cat is very bad so i was going to start there after fixing that i was thinking o2 sensor or o2 sensor but in the meantime to get rid of the problem disconnect the plug on the front o2 sensor it worked for me i have been running mine for over 2 years like that i just got to get around to troubleshooting it further but my first step is the cat
AJ

angryjohnny · 09-21-2008, 09:58 PM

Quote:

Originally Posted by angryjohnny

I had the same exact problem I disconnected the front bank o2 sensor it runs like a champ now it throws a code I know this is a temp fix for it i havent figured it out yet but i do know my cat is very bad so i was going to start there after fixing that i was thinking o2 sensor or o2 sensor but in the meantime to get rid of the problem disconnect the plug on the front o2 sensor it worked for me i have been running mine for over 2 years like that i just got to get around to troubleshooting it further but my first step is the cat
AJ

Any Luck did it work for you??

manion · 10-06-2008, 09:55 PM

yes been driving it like that for two weeks im going to change my 02 sensor first then try a cat.

angryjohnny · 10-06-2008, 10:27 PM

Let me know how it works out for you
AJ

**Jake2687** · 10-19-2008, 10:47 AM

I posted in another thread that I also have a 99 TJ that is running rough when cold. I changed the front temp sensor (anyone know if that's the gauge one or the computer one?) I've also changed the throttle position sensor and neither have helped at all. Haven't tried the O2 sensor yet, where is the one that I can unplug? Any other suggestions would be greatly appreciated.

Jeff

**Jonny Jeep** · 10-20-2008, 04:23 AM

Look down at the exhaust manifold where the exhaust clamps up to it. The upstream O2 sensor is just below that joint. Follow the wiring up to the inlet manifold where you'll find the connector.

The problem is caused by the heater circuit in the O2 sensor going bad. Here's a couple of recent threads on the subject...

http://www.jeepforum.com/forum/f9/engine-sputters-first-few-min-operation-619474/#post5861353
http://www.jeepforum.com/forum/f9/97-tj-sputter-stall-o2-sensor-612880/

**Jake2687** · 10-21-2008, 01:32 PM

Thanks Jonny, I'll have to give the o2 sensor unplugging trick a try, i'lll update after I figure it out

angryjohnny · 01-27-2009, 10:17 AM

Did the 02 sensor ever fix it for you ?
AJ