Look on fleabay/amazon etc you can get cheap OBD2 plugs, get a bluetooth one you can use an app for Android phones called "Torque" to read and clear fault codes and get other information, as well live gauges with info direct from the engine.

Alternativly, buy a USB OBD2 plug, and you can get OPCOM (the Opel garage software) which can give more indepth info and allows to alter stuff and reprogram the ECU.

When you know the fault code, you can to the garage knowing what needs doing so you wont get ripped off.

Sorry for delay in reply.

It was the wastegate seized. I freed it in situ. It has worked fine for the last several thousand miles.

I put the van on ramps. When looking up the back of the turbo you can see the wastgate actuator . It also helps if you remove the cover from the exhaust manifold.

I placed a long pry bar up between the engine and manifold from underneath and gently moved the actuator in/out. It was very stiff. ( The actuator is round and has a pipe on it)

I sprayed some copperslip into the arm that goes into the turbo and is the wastegate. This took a while and a few plastic tubes taped together. Once this arm moved freely I took it out. It drove perfect. I made sure for a few miles I accelerated hard, slow down and accelerated hard through all gears. I also kept on/off the throttle at around 1800 rpm to make the actuator go in/out and rotate the wastgeate as much as possible.

That was a year ago. Now I make sure if i'm tootling around in traffic for a long time I thrash it up the gears, making max and min boost to keep it free.

It was an easy fix.