Harper said:
An apology is due to @
Mrcento.
I know you suggested we should hold off buying a new cat until you'd had a chance to investigate the possibility of a leak causing the hunting but as you've no doubt read in the fix-it thread it's been purchased anyway. Martyn and I did discuss the further merits of buying a new cat after your post however it was decided to sod the expense and go with it anyway - just in case as per my last post here.
For the record the suggestion to just to do it and not say anything was mine and that is were this apology stems from. I should have told you in advance what was decided and I'm sorry I didn't
It's cool. Having a brand new cat on it isn't going to be a bad thing!
The problem still is that without the idle sorted, the chances of passing are still more or less zero. with the vacuum leak (and it is), the ecu can't comprehend what is happening. If that gets sorted, and it will, then with the new cat too, it should pass.
The reason for holding off on the cat was A) Expense and B) the vacuum issue could well sort it for free/cheaps and have a chance of passing without the cat as cento's have been known to pass emissions with no cat in place!
Anyways, hoping to attend next fix it meet
What i would be doing to trace issue, removing all the inlet side of things, so everything from the airbox, Throttle body and manifold.
That gives good room to inspect all the various pipes and their clamps.
Then assuming nothing is found that needs fixed/replaced mean time, renew inlet manifold gasket and check the seating of the throttle body, maybe make a new gasket for that too. refit all that, pipes etc, make sure all are clamped up and check airbox is sealing etc and take from there.