1999 Chrysler Concorde cylinder 4 misfire

Engine Performance problem
1999 Chrysler Concorde 6 cyl Automatic

Hi
few days ago the engine started to make a loud noise and stalled behind the red light after few min the engine check light went on. The mechanic said that forget about fixing it. The dealer said 400$ for diagnosis and 200 for flushing but I am not sure if flushing will help.
changing the engine costs too much. Please advise and tell me what to do. Oil change and service was always on time, but it burned oil and had blue smoke for few months but finally took care of it.
the spark plugs were changed less than a month too.

please help.

thank you for your time and answer,

yours
mary

ps. The engine is 2.7