i just got a new heavily modified evo 9 and when i inspected it evreything thing was good except that sometimes when i turn it on it will idle up and down strangely to the point where it's about turn off and sometimes it does turn off at a full stop. i took it to get scaned and the code that came up was a multiple random engine misfire (po300). so i checked it again to see if it was a bad spark plug or anything else and it seemed fine. a buddy of mine was guessing that it's probably a bad sensor. does anyone have any idea of what it could possibly be?

 

The computer can also normally identify the specific cylinder in which the misfire has occurred. A misfire is nothing more than a lack of combustion, which can be caused by poor fuel quality or metering, low compression, lack of spark or unmetered air entering the engine. OR see a tuner he should be ables to reach your ecu

 

Check your CKP/CMP with a DMM, make sure they both are working properly.

 

Good advice above. Once the misfire is detected it will shut down injectors on the pair of cylinders, that's why it runs like crap. Bad plug wires can cause intermittent misfires as well.