Last week, my 2010 5.4L with 120K km started misfiring after a long haul with an enclosed car hauler in the rain. When I started investigating the problem the first thing that was noticed was the amount of water (approx 16oz) in the resevoir after the air filter before the throttle body and the air filter showed signs of having been wet. It was decided to change the plugs and air filter where it was getting close to the recommended service change anyways. Thankfully non snapped on the way out. Initially with the new plugs (NGK's) there was an unusual shake which after we put the scanner on her, came to find out we had a bad plug misfiring. We got a replacement and nothing is misfiring now. However, I am finding on the initial startup of the day it has higher RPM's then I'm use to for about 45- 60sec then settles out to 660. The computer is all over the place in terms of how much fuel until empty its climbing and falling constantly. The gauge itself seems to be on track and fuel economy is at 12L/100km. Im thinking maybe the MAP Sensor is on its way out where so much water was sucked in? There is also a small exhaust leak which hasnt been located yet. Any ideas?

 

Did you disconnect the battery? If so, there is a lot of re-learning going on in the DTE (all its averaging calculations are gone) and also the idle. It'll all settle out after a while.

 

As a matter of fact I did. I was advised that there was some "Spark Knock" and the solution was to disconnect the battery for a bit. This did solve that particular issue. The initial startup for the day sounds like its almost going to stall, then after the higher rpms things settle out. Is it possible the MAP sensor is damaged? During our first scan it indicated in the code memory that there was intermitent sensor faults, but after the plugs were sorted out it never came back.