I own a Vauxhall Astra 1.4i 16V (2001, X Reg) and it is spluttering at 30 m.p.h, I have now been told it could be the Ignition Module, I hope this helps and sprts out your problem, I am now going to get my Ignition Module replaced on my Car, to see if it sorts out my problem!!!
Vauxhall_Astra, February 2009