hello . new to this forum.I have a 1996 xj6 with intermittent problems.when I do get codes I get the p300 (random misfire) or p300 along with the p1314. car has 130k on it. new plugs installed about 3k ago. swapped coils (used ones) at the same time as plug change. car starts every time.seems to idle better cold than hot. once warned up and sitting at a light there seems to be a miss. this miss happens with no check engine.miss also happens whenever it feels like it. winter, summer spring dont matter . once in a while it just dies. usually restarts . I also have noticed black exhaust tips like its running very rich which it may be cause the mpg really suck.I can not seem to pinpoint when its going to miss and feel like stalling. check engine is the same way.dont always come on each time there is an issue.now I have read there were some valve cover problems with these and or some kind of o rings for the valve cover .anyone had this ? Im almost sure its some kind of common simple thing . I have all ready done throttle body and egr in the past along with o2 sensors.I also might add that there are no main cats in the car (they were toast).only the pre cats are in place .I dont think that makes any difference as a year ago this wasnt an issue . hmmmmm