sti007

Hi all. Have been getting a lot of 'cabin shake' and misfire/hesitation on my 96' sti version 3 (Standard engine) The problem seemed to be worse when warm but still did it now and again when cold. No CEL have been displayed. Checked my MAF and Idle control valve and they seem to be fine. I had the plugs and leads changed this week and when the car is cold the problem seems to be gone but problem returns when its warm. The garage think its maybe the coil packs but I'm moving house in 2 weeks so cant keep throwing money at the car as I'm selling it soon. Does this sound like a coil pack problem? I have an HKS dump valve fitted, could this be causing probs, or maybe throttle position sensor? By the way, my o2 sensor was changed last year. Any help appreciated.