from what I can find
In 2006, the turbocharged engine (powering the Forester XT) was awarded International Engine of the Year. This engine is also used in the Subaru Impreza WRX, as well as the re-badged Saab 9-2XAero
So the new parts are. Variable valve-lift system that bumps horsepower from last year's 165 to 173, while turbo Foresters have a higher compression ratio and redesigned intake and exhaust components for a 20-hp boost to 230 and cleaner tailpipe emissions. The manual and automatic transmissions have also been updated for better performance, as has the suspension. Interested shoppers should also note that Subaru has simplified the Forester's trim levels for the 2006 model, Subaru gave the SG a facelift, using redesigned headlights, tail-lights, bonnet, grille, front bumper and side-moldings. I have to admit that sound's great So not sure why it seems to have the fault. Sorry I couldn't narrow anything more down. And it's the same with the Imp's all my Impreza's I've had to travel for them. So you're not on your own with that part of buying one ;)