you can get a low cost fault analyser/code reader that should spit out an engine management fault code. see here
http://cgi.ebay.co.uk/U380-OBD-2-II-...item3ef0d29d25
this would confirm the dealers diagnostics- alternatively you could use it to clear the fault code and see if it reappears.
I used one of these to successfully detetct a faulty coil pack.