MK4 Escort with a N/A 2.0 Zetec running a DESK ECU.

Always had quite a stutter when initially applying power and also when changing gear (any time when power is applied from zero throttle really).

Recently its started pinking under load at mid to high revs in 4th and 5th.
Quite odd as I didn't think pinking would be possible with this setup, and it doesn't happen at low revs or gears either..... can't even provoke it at any other times and it doesn't even do it consistantly...any ideas?

Could an air leak casue this?