Hi,
I'm sure people are really interested :-], but I changed the HT leads on my Astra and it made a world of difference. [Note to self: back to basics to begin with before you go on a 'guessing spree']. The guy I bought it from said he'd changed the HT leads, and to be fair they didn't look antiquated, but were obviously not carrying the charge properly - as detected by removing each plug lead in turn and listening for the change in engine noise.
I'm still not convinced it's running to an optimum level of performance, but at least it's driveable now!
Ta again.
Garry