Check ENG light ( Code 354 )

For last three day I been try to fix the problem with my 98 GT 4.6.
I keep getting a check ENG light and when I use the code reader I receive a code #354.The ford shop said it was the number 4 cylinder not receiving spark. So I changed the spark plugs and spark wire and replaced one of the igition coil. The car when driving will bog down like it's has lose of power and start to drive slow and sluggish. Also I did chang fuel filter. Can you help me :)

I have a 98 gt that had a similar problem...I found a small leak in a heater hose on the back left hand side on the intake and firewall that
was filling the plug hole with antifreeze causing plug to short and not fire..