I have an 04 WRX that keeps throwing a cylinder 4 misfire code. Symptoms are a rough idle (no loss of power while throttle is pressed) and CEL on the dash. I've replaced the plugs, wires, and swapped the coil packs around with no progress on the rough idle. Also rebuilt the stock blue injectors. Any advice I before I have to take it in would be appreciated. Not many good garages around here.