fair play. there could be underlying issues with the 1.7 as well bud. they are prone to turbo problems too, as well as sensors.

but as said above, without checking it over its hard to say if its a mechanics fault.

ive seen many a vauxhall come in, stay in for months waiting on parts, then finally get the parts and leave, and it could come back in weeks later, never usually for the same problem though. but not every garage will be that lucky.

do you know what all has been done to this van then if its been in 4 times and still in?? surely they have a reason for keeping it in??

if they couldnt find a fault they would hand it back to yas and tell you to bring it back if fault persists.