I was told to install NGK BUR 9s on all 4.when I do that I have problem starting and bad idle when cold. With the Trailing with 7s and Leading with 9s car runs great.

Car has intake and full 3" also good gas new wires igniter fuel filter in good working condition. Car also sites most of the yr. Right now I have 9s install but not P BUR9EQ i was told the P is not that good...Thanks for any help...