i have a 99 mustang gt it started running rough awhile back and just kept getting worse I pulled the spark plugs and the drivers side they were all black like they're running rich and the other side were white like it was running lean. so how could one side be running lean and the other rich? so i took it to the dealer and they said it was missing on three cylinders and needed three new coils and new plugs so i buy all that ****, install it and it still misses but now it got so bad i cant drive it. i can start it and it'll run up to about half throttle if you give it any more gas it bogs down. has anybody ever heard or seen anything like this?

 

I think you should start with a compression test.