98 XJ with 4.0L.
This problem started out as occasional and only at higher temps, but has increased in frequency over the last year or so to where it now happens every time.
It will start fine in any temperature, but when warm (mid 80s or higher ambient, or if engine is still warm from previously running) about 1 minute after starting it will run really, really rough for about 5-15 seconds. Nearly zero power, stumbles and sputters, popping in the exhaust. Going WOT will cause it to fall flat on its face and nearly stall, while pedalling it between 0-50% throttle seems to bring it out of stumbling more quickly. That could just be coincidence, though.
When it comes back out of it, the engine will continue to run just fine until it is shut of and restarted again (although it may be down just a little on power for a minute or so after the stumble).
A bit dangerous, as it's acting up is timed to occur just as you'd be pulling out into traffic from a parking lot for example.
No codes. I've done some shotgunning. Throttle body cleaned. IAC was cleaned, then replaced. TPS replaced. Exhaust, including O2 sensors were new 6 years ago, but I've since replaced both O2 sensors again (NGK). Front one was completely covered in carbon. Understandable, I suppose, as it tends to pop in the exhaust when it is acting up (fuel, but no spark? excessive fuel with or without spark?).
This is a WAG, but the timing of the problem seems to possibly indicate something going funky when the system is switching from an open-loop starting mode to a closed-loop running mode. I honestly don't even know if/when that occurs.
I've found numerous threads on rough running being caused by a number of issues, but nothing this temporary.
Any suggestions?
Thanks.
This problem started out as occasional and only at higher temps, but has increased in frequency over the last year or so to where it now happens every time.
It will start fine in any temperature, but when warm (mid 80s or higher ambient, or if engine is still warm from previously running) about 1 minute after starting it will run really, really rough for about 5-15 seconds. Nearly zero power, stumbles and sputters, popping in the exhaust. Going WOT will cause it to fall flat on its face and nearly stall, while pedalling it between 0-50% throttle seems to bring it out of stumbling more quickly. That could just be coincidence, though.
When it comes back out of it, the engine will continue to run just fine until it is shut of and restarted again (although it may be down just a little on power for a minute or so after the stumble).
A bit dangerous, as it's acting up is timed to occur just as you'd be pulling out into traffic from a parking lot for example.
No codes. I've done some shotgunning. Throttle body cleaned. IAC was cleaned, then replaced. TPS replaced. Exhaust, including O2 sensors were new 6 years ago, but I've since replaced both O2 sensors again (NGK). Front one was completely covered in carbon. Understandable, I suppose, as it tends to pop in the exhaust when it is acting up (fuel, but no spark? excessive fuel with or without spark?).
This is a WAG, but the timing of the problem seems to possibly indicate something going funky when the system is switching from an open-loop starting mode to a closed-loop running mode. I honestly don't even know if/when that occurs.
I've found numerous threads on rough running being caused by a number of issues, but nothing this temporary.
Any suggestions?
Thanks.