2007 JK – P0300 misfire under load, stalling, lean codes, runs fine at idle
Hey all—if anyone happens to be near Meridian, ID and would be willing to take a look or help diagnose in person, I would truly appreciate it.
I’ve also uploading a video with this post showing how it idles.
Looking for some help diagnosing an issue that came up after doing some maintenance. I’ve done quite a bit already and trying not to just throw parts at it. When I purchased it, it wasn't throwing any codes, but it could barely steer due to the missing sway bar links and needing a steering stabilizer, but these problems didn't seem to be present.
Vehicle:
- 2007 Jeep Wrangler JK (3.8L)
Recent work completed:
- Replaced spark plugs
- Replaced plug wires
- Replaced ignition coil (aftermarket ECCPP), then swapped back to original coil
- Replaced valve covers
- Replaced serpentine belt
- Replaced both front sway bar links
- Steering Stabilizer
Current symptoms:
- Idles fine (let it run 30–45 minutes with no stalling)
- Under load:
- Accelerates okay up to ~30–35 mph
- Struggles to go faster (feels like limp mode)
- CEL starts flashing
- Severe loss of power (can barely maintain ~10 mph)
- Engine will stall while driving
- After stalling, it won’t restart immediately but will after sitting a few minutes
- Engine seemed to get very hot during a short drive (but the temp gauge stayed in the middle)
- Brake light flashed intermittently during the issue
Codes:
- P0300 (random misfire)
- P0131 (O2 sensor low voltage)
- P0137 (O2 sensor low voltage)
Additional info:
- Cleared codes after swapping coil, P0300 returned but not seeing the O2 sensor codes but I haven't tried driving it again.
- Runs smoothly at idle, no major sputtering
- Issue only shows up under load / driving
- Coolant level is good
- No obvious vacuum leaks seen yet, but haven’t done a full spray test
- This all started after the recent maintenance listed above
What I’ve ruled out so far:
- Ignition coil (swapped back to original, no change)
- Basic idle issues (runs fine at idle for extended time)
Appreciate any insight—feels like I’m close but want to be smart about the next step.