A while back I posted a problem with misfire codes.....mainly PO300, 01 & 02 on my 2002' 4.0. It was suggested I needed to replace the coil rail which I did. I bought an OEM Mopar unit as was suggested and put in new APP 985 plugs as well. All was well for a while then I started getting just a PO301 code. I cleared to see if it would return and it did. A couple of times I got a bad engine miss with the CEL flashing. The codes were PO300 & PO301. The thing that puzzles me is that when I turn off the engine while it's missing, clear the codes, and start it back up again it purrs like a kitten and runs well for awhile until the PO301 pops up again! I had a PO122 just once and never returned. I just can't help but feel If something was really wrong it would be there constantly until corrected? I replaced the ECM last summer when the engine would not start at all! I'm beginning to wonder if this could be the problem? I'm located in the UP of Michigan and knowledgeable Jeep Wrangler mechanics are scarce! The closest Jeep dealership is 60 miles away so I'm pretty much relying on help from this forum before I give up and take it to the dealer! Any suggestions?