The rough running is probably caused by the +4s, they are not OEM. Search the forum for the stock Bosch plugs (I just replaced mine 3 months ago at 80k, got the best price here). The stock ones are not cheap, more than +4s, but as you will see if you search the forum, the +2s and +4s have caused people all kinds of problems. Before you go doing something more expensive like an MAF, I would spend the $150 and get new OEM style plugs.