Northwood 1.7 problems

I just popped my 1.7 Mobile Northwood into a spare Abit AI7 and got it up and running, just to see what it could do. But after booting up, the chip is recognised as a 1.7, but is clocking at 1.2. Any attempt to push it up to 1.7 causes instability. It still runs ok, and is VERY cool (29c at 1.4 and 19c ambient) (cannabalized from my dead laptop). Has anyone encountered this before?