My 2002 2.7 WJ has a misfire. Engine starts fine and idle is smooth, but as soon as any throttle is applied the engine starts to miss on what feels like one cylinder. The misfire is worse in "cold" weather (under 10 deg C here in Spain). The car is reluctant to rev up to drive away until it has been running for a minute or so. When the engine is warmed up the problem is slightly better but is still there especially at 1500 rpm. When stationary and warmed up the misfire is randomly present - if it's idling smoothly and I rev the engine slightly (1200 rpm) the misfire reappears at idle - leaving the engine at idle for 5 secs or so the misfire goes away. I've changed the fuel filter, cleaned all the visible sensors and checked all the fuel lines for weeping. After changing the filter I vacuum purged the air from the system at the bleed port. None of this made any difference to the misfire. When my daughter owned the car she had it looked at by a genuine Jeep dealer in the UK who carried out a diagnostic and injector leak back test with nothing found. Any suggestions most gratefully received.
