My Explorer is giving me KOEO code 335 and CM code 214... according to FFI.com: 335=PFE or DPFE sensor voltage out of self test range 214=Cylinder identification circuit failure Can anyone help explain this? Background story: 94 Explorer, 2dr 4WD, 145K mile daily driver. Stock. When I bought it I put two new cylinder heads in due to a crack in one (850 miles ago) I recently started seeing the CEL come on occasionally when the motor is up to temperature and I get on the throttle hard, like accelerating on the highway. When I slow down, or sometimes even if I don't, the light goes out. No driveability issues or noticeable change in motor performance. The only other hiccup on the car is that when I cold start it, sometimes it idles rather rough (fluctuates and some vibration, sounds like it is missing) for maybe 5-15 seconds. I generally let it warm up, blip the gas a little, and it clears out and runs great after that. My snowmachines do the same thing when there's a bit of water in the carb and force of habit makes me treat the car the same, easing into the throttle till it warms up and clears out. Please correct me if this a bad thing to do. Friday after work the light came on seconds after I started the car (drive to work was fine). No other problems besides the light, took it home and poked around and couldn't find anything obvously wrong. I tore the whole dash apart and scoured the engine compartment looking for a "trapezoid shaped connector that can handle 16 pins" and ignored the obvious STI/STO connectors because they didn't fit the Chilton book's description. I gave up, drove to work yesterday morning, didn't see a CEL all day. Today I was running errands and one start it came on again and stayed on. So, I browsed these (awesome) forums and found fordfuelinjection.com. I identified the connector, read the codes (Chilton didn't list either of the codes I got) and here I am. So! What do these codes mean, should I even bother with them considering the car runs just fine, and if so how do I go about fixing this? And on a side note, this makes three times that book has failed me with missing or incorrect info. I seem to recall Haynes manuals being better. Recommendations? Thanks! -Rhen EDIT: Could part of my problem be plugs? I changed them for expensive Bosch Platinums the day before I took the car in to have the heads swapped, and the mechanic put in new Autolites and kept my Bosch plugs. He says he gapped the new plugs and told me correct gap without missing a beat, so I assume that's correct, but could these plugs be causing trouble? Now that I think about it, I also changed the oil just before taking it in with Mobil 1 and he did an oil change too. EDIT 2: What about this? http://www.niehoff.com/techtips/n_sen.html Might explain the the code 335 but not 214.