Hello and thanks for reading.
I have a 1999 Mercury Grand Marquis which I recently bought used with 120K miles. The check engine light came on, and it was missing badly. I took it to a guy who read the code and said it was a misfire on #4. He replaced the coil pack and the plug on #4.
All was great until about 20 miles later. It seemed to be the same thing with the bad miss and the check engine light. I went back, and this time the code said it was a misfire on cylinder 5. He inspected the coil pack, and checked the plug. He cleared the code and said all was well.
I still have the bad miss, and the check engine light is on again. Do you have any suggestions for me about how to fix this?