Sounds like this could be the issue then, I guess blocking the EGR pipe is only masking a fault that is still there. I would probably get whatever is wrong fixed first, get another emissions test done then go from there!

If you do have unburnt fuel passing through the exhaust, it will knacker the cat in no time too. Check the t-piece in the vaccuum lines, its under the coil pack if I remember right, these often split causing all sorts of running issues.