could also be plugs, coilpacks, or even your MAF. what mileage does the car have?? if your plugs or coils are original it might be time to change them out, these cars have coils that dont last very longs, also with the mods you have should look at getting colder plugs if you havent yet...kind of going through the same problem and am in the process of figuring out what it is....
The car has almost 98k miles on it right now... not sure if the coilpacks are original. Perhaps those and a new set of plugs should be my next upgrade. Are these things cheap? Easy to replace? I'm sure sparkplugs I can do but i dont even know what a coil pack is.