P0174 Cadillac - What is the most likely cause for this code?

Question

Car is running but with a very rough idle. Spark plugs have been changed and are new - this did not solve the idle issue and the check engine light came back on after the plugs were changed.

Answer 1

P0174 Fuel trim lean Bank 2

Vacuum leak , what you have is a vacuum leak, when a vacuum leak occurs it creates higher idle and sometimes rough idle, and sometimes depending on the vacuum leak hard to start especially when cold.The most common vacuum leaks occur at the PCV hose or the valve.