Hello. I'm new to this forum, but here goes. I have a 2000 Explorer, 4.0 SOHC with about 100,000 miles on it. About 3 months ago, I was getting codes Po171, Po174 at the same time. My truck was "chugging" at idle, so we thought it must be a miss, bad plug, etc. At the advice of a self-proclaimed mechanic, we changed the plugs and wires. They had at least 30k on them, so why not? For about a month's time, all was well. Then the CEL came on again. This time, Im getting codes PO171, PO174, PO304, and PO442. PO171 and PO 174 suggest a rich or lean fuel/air ratio. PO304 suggests a misfire on Cylinder #4. inspection of the plugs/wires show that they are in good condition since I recently replaced them PO442 suggests a small leak in the EVAP system. And from what I have read, PO442, is the "mechanic's nighmare" Just to give some insight, the vehicle "chugs" badly at start-up, and now it chugs sometimes while moving. I used some fuel injector cleaner and installed a new gas cap (the old one was, well, old), and I'm looking for some additional direction as to what all this could mean. I'm not even sure they're altogether related. Any assistance would be appreciated.