What causes the CODE PO316 on 2003 Lincoln Town Car

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
Originally I had a code "misfire #7". I had blown a spark plug on cyl #3 3 months earlier. I replaced all of the plugs and when replacing the coils and injectors I moved the injectors right and the coils left hoping the miss would move and I could tell what was faulty. Bingo, misfire #8 which told me the injector was bad. I removed them all keeping track of which one came from which cylinder. I found a video on-line how to clean and test them and I did just that. The suspected one was plugged but cleaned up pretty good. I replaced it into cylinder #5 since it is easy to get out. Started up and ran great for 5 minutes then gave a code "misfire #5". I replaced that injector and it runs well for about 8 miles and then flashes the wonderful #316 code. Any comments? Also my alarm keeps going off and the DOOR AJAR light stays on? Any help on that? My car is possessed!
(1) Answer