Hello. That era Subaru could have a problem with the fuel injectors leaking, especially in cold weather. Also, ice can form on the tips of the fuel injectors. Other common starting problems on that era also sometimes seen on a Subaru Impreza WRX STI for sale by owner is the engine coolant temperature sensor. This sensor can go flaky without necessarily triggering a CEL/MIL, and it can cause starting problems. The same thing can happen with the cam position sensor. Let me know what you find out!