Like the title says, I have a '98 Jeep Cherokee with the 4.0L and I'm having trouble figuring out what is causing it to run very rough and misfire a couple minutes after you start it. All the usual suspects have been replaced; fuel filter and pump, coils, wires and plugs and it still does it. It's weird though that if you start it up, let it run for a bit and start driving, it's fine and then after couple minutes, it does this. If you have a good stretch of highway, you can get it to stop by just flooring it and taking it up to 65-70mph. Even if you finesse it, it still misfires during this. It just slowly loses power and if you only give it a little more gas, it stumbles and backfires worse.

Anyone have any ideas? They would be greatly appreciated and thanks in advance.

 

how old is the cat?it is possible it could be clogging,get under the jeep and hit the cat hard enough to see if you can hear anything rattling,other things that can cause this are,iac,tps,cps could also but they would be anytime not just after it warms up.

 

I'll give that a try. Any reason why it would be when it wouldn't be all the time with the cat and not be fine right away or after a while?

 

I gotta agree with the cat. If you dont have good in and out flow then it will stumble and backfire. My old truck would periodically backfire so I tuned it up and didnt fix it. Then replaced cat and it worked.

 

It is hard to say with the cat,but if it has loose material in it that restricts the flow as air flow increases,it is also possible that your cps once it gets warm the resistance on it increases and causes what you are describing,do you have any codes.on yours you should see something like o2 sensor,even if it is ok a misfire will cause it to be out of range and send a code.