I'll start with a little background on the car. It's on 03 Evo 8 GSR, with the following mods ;

-Injen intake & UPIC
-Samco BOV
-HKS TurboTimer
-Walbro 255 Fuel Pump
-Hallman pro MBC
-Megan Catback, Test pipe, Downpipe
-Internally ported/externally ported/swaintech coated exhaust manifold/also with porting
-Ported/Coated o2 Housing
-Ported/Coated 10.5 Hotside
-Ported Intake Manifold
-Ported 65mm Throttle Body
-PPI LICP-
-XS power FMIC
-Jester E-flash.

I was on my way to work, cruising on the highway about 70 mp/hr when the car feels like it started to vibrate and it literally sounded like a Harley motorbike, is the best way i can describe it. The SES light came on, so i figured something broke, so i started to pull to the shoulder when the SES light went off, but the vibration and noise stopped as soon as i let of the throttle. The SES light was not on long enough for me to get the error code, so i have no starting points to figure it out. The same thing happened on the way home from work on the highway.

Anybody have any suggestions on where to start? I have read multiple threads, but no one has the same issue as i do where it happens, stops and doesn't appear again for sometime. The only thing i have to go on, is that two days before i got caught in some rain and through a misfire in cylinder 1 code but the next morning it had cleared itself so i thought nothing of it.

 

finally got a code to work off of. The dreaded p0300 random misfire. All the threads I have read don't have the same issues as mine. I gapped the plugs last night and now the car doesn't misfire but I still get the code.

Any ideas or suggestions?