03 AP1 Misfire/Car shutting off
 

Here is a little backstory on my car, 2003 AP1 with 138k on the clock. I had misfire codes back in 2017 and was determined that I had bent intake valves and had my head rebuilt with AP2 components back in May 2017. Fast forward 2 years, the last few months my CEL returned and is giving me P0301, P0302, P0303, P0304, P0300, and P1399 codes. I’ve noticed that when I start my car, I hear a loud vacuum sound on startup that goes away within a minute. Also on cold starts, when I put it in 1st gear and come to neutral to come to a stop, the car shuts off and all lights on dash light up. I try to start it and it has a long crank but eventually turns on.

My spark plugs were changed 40k ago, coilpacks replaced 40k ago. Never changed injectors. The car has a K&N intake, berk test pipe, and tanabe medallion exhaust. All help is appreciated thank you!

Bump*

Another issue I’ve noticed today is the car seems to die a lot more driving with the AC on and coming to a stop to idle.

Might be caused by excessive drag by one or more accessories such as your AC compressor. Just a thought. Have all those components including your alternator checked for drag/stiffness in their pulleys. Check all the vacuum lines running from the air pump and secondary pump to make sure there are no loose ends.