Hi Clare... OK, well that is a start. I am very surprised that despite getting the spanner light coming on, you haven't got any error codes on your diagnostic check. The Spanner Light usually means that there has been a fault generated, and the ECU should have it stored. Did you get the check done on a Vauxhall-friendly machine? I ask this because some of the more intricate error codes, which are unique to GM & Vauxhall, will only show up on either a Tech 2 or OpCom unit, or even on a Vauxhall Dealer Diagnostic Unit.
As you have the 1.6 petrol unit, I am really not the best person to ask about this engine specific condition, as I run a 2.0 dti diesel Zafira, which has its own very strange peculiarities!
You need to hope that someone like Marks 152, who I believe runs a 1.6 himself and is extremely knowledgeable in this area, has picked up this thread and will run with it for you. You might even want to check his posts and possibly prompt him with a Private Message if he hasn't picked this posting up within 5 or 7 days. Good Luck to you - I'll keep my fingers crossed that you can get it sorted quickly! Cheers... Robin