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engine hesitation runs rough until operating temp

10K views 22 replies 10 participants last post by  Jerry Bransford 
#1 ·
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?
 
#4 ·
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.
 
#7 ·
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.
 
#8 ·
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
 
#12 ·
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
 
#13 ·
#16 ·
i have a 97 wrangler 2.5 And Ive been having these problems for a while now and i have replaced the bank 1 o2 sensor, cps, ad the distributor and it just has gotten worse. Im tired of throwing money at it and i have heard that reflashing the pcm could fix this problem. i hooked it up to a scan tool and went through all the sensors look fine even when running rough. except for the fuel sync it says the fuel sync is lost while running but ok with the key on but not running. I would realy love some help
 
#17 ·
I have a 97 2.5 Tj and have been having the same problems i have hooked it up to a scan tool too monitor the sensors and it was throwing a code for the csp and it did look a little weired so i replaced that and the problem ended up getting worse after i replaced the csp it brought up a code for the ckp i also noticed that the fuel sync wast lost when running so would that mean i have a problem with the injectors or would it be a timing problem.
I would really love some help to this im tired of throwing money at it
 
#19 ·
Keep in mind that if the problem only occurs when the engine is cold/was just started, it's not caused by a bad O2 sensor. The engine computer doesn't even look at the O2 sensor output until the engine has started to warm up. Did you read the entire thread and notice the suggestion made in the #3 post above?
 
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