Subaru Impreza 2002: Throttle response too sensitive

SINCE new my daughter's 2002 Subaru Impreza has been ``hunting'' at low speeds in low gears, which is very frustrating in peak-hour stop-go traffic. It feels as if the throttle response is far too sensitive. The same happens at 100km/h on cruise control. Four Subaru service centres say there's nothing wrong and to just use more injector cleaner. I wish they'd drive the bloody thing and ignore their computers. My other daughter's 1996 Impreza had a similar problem and it was fixed, but the service manager who identified the problem is no longer around. That car also has a lot more power than the later one. Any ideas on who to turn to? I've now canned thoughts of having a third Subaru in the family.