I've got a year 2000 S2k with a solid lit CEL.

102,156 miles. No mods other than an after market air filter.

I changed the oil (Mobil 1 Synthetic) and replaced the oil filter, but still felt weird vibrations from the engine and reduced power when I accelerate. It felt like misfires, so I pulled the codes.

P1399 (spark plugs?)
P0301
P0302
P0303
P0304
P1456 (loose gas cap or leak in vacuum system?)

Any advice is appreciated.

Much thanks!

 

P0301-304 = misfires on all cylinders.

Change all of your spark plugs, 100k is the replacement interval for them anyway.

 

spark plugs, and could need VA if it has yet to be done.