I recently have parked My 02 WRX Wagon Auto due to a tranny problem when ever i hit the gas it stutters and will never grab. if done slow i can accelerate to TOPS 40mph,( found that out trying to get it somewhere safe and close) I recently had replaced the rear diff as i had a problem wih it chunking and binding up, anyway this all happened very suddenly from being parked to taking a quick drive somewhere, with no problems to parked for a few hours, and immediately,when i started it extremely bad, not driveable. car shudders and will not grab, revs fine, even in D not moving, my car slightly jolted forward under complete brake. as if the torque converter was grabbing than releasing. tried running through gears keeping in 1 or 2 but it does not matter what gear. it seems to shift fine through the gears just wont grab.
i dont know what this is, very tortured from it since me driving my car is my life.
PLEASE IMPREZA DRIVERS UNITE HELP ME PLEASE
AN Ultimate Subaru FAN,
James Kavanagh

 

This could be a loose spark plug. I've had similar symptoms. It would rev fine in neutral but once under load it would just shudder a lot.