My 2002 wrx has a history of misfire codes (e.g. P0302) every 30,000 miles or so and the solution has always been to replace spark plug. Right now, it has P0302 code when the car is driven for half an hour or more. If I turn off the car for a while, it runs fine again.
Also, the idle speed does not increase when A/C is turned on. I wonder why.
What is the mechanism that increases the idle speed when A/C is turned on? Does the A/C button sends a signal to the ECU to increase idle speed, or does the ECU senses the extra load on the engine and increases idle speed to prevent stall?