I have an 06 grand marquis LS. That's having multiple misfire underload only in drive. I recently changed the spark plugs not too long ago. And I use a fuel system cleaner every few months. It starts and idles fine. Initially, once you put it in drive, it'll take off Fine most times, but then it sputters very badly And Lose power and it throws a multiple misfire code. Some days It runs perfectly fine with small missfire here and there. Please help.. I love this car and would love to get her fixed asap. Thank you.