Bad hesitation/backfire through intake?

[nitrojunkie1029]

Ok guys. I have a 96 XJ with 180k on it. When it's cold like after it's started for the first time that day, the ambient temperature doesn't matter, I'll go to drive it and as the rpms get to about 2-3k it will spit and sputter and it sounds like it's backfiring through the intake. It's never done this before and after I drive it its fine. I am stuck with what I should try to fix. I'm thinking a seafoam treatment through the intake and try to clean the carbon out and off the vavles , but I want to hear what you guys have to say. Thanks

[4.3LXJ]

It does this only when the engine is cold?

[nitrojunkie1029]

It does this only when the engine is cold?
Yes. It feels like it just looses power and then spits and sputters and what sounds like backfiring through the intake (not 100% sure on the backfiring) if I drive it hard it doesn't really do it as often. And it goes away completely after it gets hot. As soon as it cools down it does it again

[4.3LXJ]

Has it been a long time since you changed our O2 sensors?

[nitrojunkie1029]

Has it been a long time since you changed our O2 sensors?
I'm not sure when they were changed last. They haven't been changed in the 2 years I've owned it... should I start there?

[4.3LXJ]

Since it is temp related, I would start there so you can make sure your engine is getting good data. After that, if it is still doing it you might look at the coolant temp sensor and throttle position sensor. But since the engine runs OK when warm, I don't think the throttle position sensor should be bad, but we won't know until you get good data coming to the ECM

[nitrojunkie1029]

Alright. I'll keep this thread posted. Thanks!

[OldFaurt]

Ok guys. I have a 96 XJ with 180k on it. When it's cold like after it's started for the first time that day, the ambient temperature doesn't matter, I'll go to drive it and as the rpms get to about 2-3k it will spit and sputter and it sounds like it's backfiring through the intake. It's never done this before and after I drive it its fine. I am stuck with what I should try to fix. I'm thinking a seafoam treatment through the intake and try to clean the carbon out and off the vavles , but I want to hear what you guys have to say. Thanks

When it is cold, before you start it, pull distributor cap and see if it is damp inside!

Cheep fix, worth a try?

[bigjim350]

A backfire through the intake usually is caused by a lean condition. I'd start with o2's

[Cheromaniac]

Ok guys. I have a 96 XJ with 180k on it. When it's cold like after it's started for the first time that day, the ambient temperature doesn't matter, I'll go to drive it and as the rpms get to about 2-3k it will spit and sputter and it sounds like it's backfiring through the intake. It's never done this before and after I drive it its fine. I am stuck with what I should try to fix. I'm thinking a seafoam treatment through the intake and try to clean the carbon out and off the vavles , but I want to hear what you guys have to say. Thanks

A seafoam treatment would be a very good idea. There may just be enough carbon deposits on the intake valves that are causing them to stick, which would explain the rough running and backfiring through the intake.
A lean condition could cause the same symptoms, and the most likely reason is clogged injectors, so it would be a good idea to treat the fuel system as well. If that treatment works, I'd repeat it on another tank of gas to clear out any remaining deposits.
You might also want to go on a 20-30 minute drive on the highway, keeping the engine between 2500-3500rpm, to blow some of the cobwebs out of the tailpipe. The engine will probably run smoother afterwards.