2004 Jaguar Vanden Plas check engine light

Multiple miss fire codes.
Runs a bit slugish idles a bit rough after warmed up. Wants to kill when backing up or moving forward slow.

had 2 different answers.
1. Flush the fuel injectors ($400) Or try sea foam. (Tried sea foam)

2. Spark plugs ($350) Are those magic plugs?

Would like to fix the right thing on the first try without having to fix 5 items to figure out which one is the real problem. (They do this to me every time I go in)