I just changed the thermostat and coolant temperature sensor in my 4.0 and now it runs rough and the p0303 code popped up. Could any one tell me what's causing this? thanks!
I obviously don't know exactly what happened in your case and I was just trying to get going in the right direction. But I suspect you changed your parts, then let the Jeep idle while you check for leaks ect. I would guess the Jeep ran ok at first then you likely turned it off and restarted it and that's when you got the code and CEL and rough idle. I would also suspect that the Jeep starts and runs fine after it cools down.
Once the number 3 injector gets hot, it vapor locks and stops firing and that causes the rough idle situation. It also causes that code which is a # 3 injector misfire code. You can google search the code and find a lot of information on it. Apparently it was a pretty common issue. Mine would only do it when I ran it about 20 minutes, stopped it and then restarted in a short period of time.
Replaced with new sensor and made sure it was "german torqued" down in there. Works good now. thanks for the help
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