Never,
Try this. Disconnect the Air Flow Meter plug and start the car and just let it idle. Check Engine light will be on.
Does the car idle correctly (600 RPM with minor fluctuations) and rev smoothly. Its your Air Flow Meter that's stuffed if you have a MY99/00. $191 for a new one.
Just in the process of changing mine as well.
Have a look in this thread.....
http://www.perth-wrx.com/vb/showthre...ighlight=meter
J