to add to what KA24Tech just said - did you check the spark plug to see if it was loose? when i first bought my altima 3 years ago, for the first three days, i couldnt figure out why the spark plug wires wouldnt stay on. i went to buy new plugs and found out that the spark plug wire in question was connected (sometimes anyways, lol) to a very loose spark plug. the compression was pushing by the plug and unseating the wire. tightened it down and the problem was gone...