06 Pacifica misfire
 

I have an 06 Pacifica with 210k it runs fine while I'm driving good girl mileage but once it idles for a few seconds it missfires on cylinder 4 .its not the plug,injector or the coil at first it only did it every few weeks then all the time. I have checked the harness for any cuts it was good I noticed if I disconnect the battery for a while it will run fine for about 100 miles and idles as it should could it be the ecu? I also noticed my a.c. quit working and only the floor vents are working not sure if it's just a coincidence or not. The only code I get is a cylinder 4 misfire that comes and goes

same issue with my 05 touring pacifica , one thing i learned was that ONLY O.E.M PARTS ARE to be in this vehicle , my pac is so freaking picky and finicky now i buy dealer or rock auto o.e.m and install . could be low compression on that cylinder? could be a bad ground?