Water or oil may enter into the ignition coil cover and the spark plug bore, causing a misfire and illuminating the Check Engine Light. A coil with improved water and oil sealing is available and should be installed.Google+
Car Problem Reports
Ford Thunderbird Revised ignition coil available with improved water and oil sealing
Ford Thunderbird Problem
Average Mileage: 34,666 mi (24,000 mi - 50,000 mi)
Visitor, 2003 Ford Thunderbird, 30,000 mi
Oil on coils
Visitor, 2005 Ford Thunderbird, 50,000 mi
About every 5000 miles one of those coils fails. The Dealer is replacing them under the extended warranty on the coils, but Ford won't authorize replacing them all a once. They only authorize replacing the one that failed, so I'm stuck going back every few thousand miles when another one fails. I'm at 50000 miles now and the 4th one needs replacing. This has been going on since 35000.
Same old shXX.
Misfiring at idle and higher speeds.