IMO, I'd say all of your codes may be related, but I don't know enough about your car. P0171 is the lean code yes, and probably caused by your Injen CAI
which isn't reading the MAF Sensor correctly. You can try the hybrid mod, get another Intake
like the TPR, or get a fuel computer to adjust the A/F ration. On P0301, running too lean can cause a misfire, simple as that.
Now I need to ask how many miles are on the car. Did you have a check engine light before the install of the Intake
? If not, did the CEL come on soon after the install? Is the P0420 code a stored trouble code or a pending trouble code?