01 Taurus misfire on #4 AGAIN!

I have a 01 SES with the flex fuel engine. It has 52k mi on it It has been in to the dealer 3 times for misfire on #4 cyl. 1st they replaced plug and wire, and it worked for three months. The second time they replaced the #4 injector, and it worked for two days. This last time i took it in and it stoped doing it. The dealer cleared the code, and it did not come back. Any one ever hear of this? I had to have the computer reflashed at 30k because the car would not start. Could it be the computer again?? :banghead: Thanks for the info.