Hello, I am the owner of a 2002 Honda Civic LX. (151,XXX) When the car came into my possession, I knew it had a bad water pump. Turned out to also have a bad head gasket. 5 1/2 months later, I get just about everything put back together but accidentally break the plastic box with filter that’s directly on top of intake which resulted in me buying a cold air intake. (Didn’t have most of it to begin with) so the time comes and I start the car and it automatically revs to 2,500 it will hold for half a second then go back down. A couple times, the idle normal, but a little low. I noticed a popping in the exhaust (which if I’m not mistaken means the air-fuel ratio is bad) It will then instantly shoot back up and repeat. I have new spark plugs and ignition coils. It does NOT have fresh gas atm. I have an OBD2 and CAN code reader and it shows me P0300, 301, and 303. The only thing I can think of is buying another valve cover gasket kit with the seals on the inside in the cover. (I previously bought just the valve cover gasket by its self. Thank you for the help!