P0420- Cat system efficiency below threshold, bank 1

P0340- Camshaft position sensor- A circuit(bank 1 or single sensor) circut malfunction

P0335- Crankshaft position sensor- circuit malfunction

P0300- Random multiple misfire

now i have a catless 3" tbe, so that explains the 0420 code, but i started having the misfire as soon as i put my down pipe on. replaced the plugs a bunch of times, gapped to .28 everytime. any help would be great

 

well like you said your catless, so count out the po420. your seeing a code po300 because the ecu can't see when to fire due to the crank and cam sensor codes. check this TSB-07-11-001
DATE: January, 2007

MODEL: 2002-07 Lancer 2.0L
SUBJECT:
HARD TO START ENGINE DTC P0340 (and P0335)

PURPOSE

The engine may be hard or impossible to start and MFI DTC P0335 and possibly P0340 may be stored due to abnormal wear to the camshaft position sensor support. Oil grooves have been added to the camshaft position sensor support to improve lubrication.If a customer has a vehicle with the above condition, replace the camshaft position sensor support with the new part listed in the PARTS INFORMATION section of this bulletin.
there is also a tsb for the p0300, but fix this first and recheck

 

only thing about that is, its never ever started hard. not when it was cold or anything, starts up exactly the same everytime.

 

it may be worn enough to cause those codes intermittently, but not worn enough to cause major concern. whenever trying to diagnose a issue always start with a little research for any tsb's or service messages. it will save you time and money. check out the sensor to see if it is worn, and you can rule that out if it's not and go from there.