reading fault codes (paperclip test)

[GT250]

hi all, back with another question i can't makes head nor tail of,

corsa 1.6 16v (W reg - 2000) i'm getting poor mpg and the car shudders a bit at tick over so wanted to look at any possible fault codes.

have looked up via google, and having the 16 pin connection in fuse box, bridged pin 5 & 6, now i only appear to get codes when i start the engine, first off it gives around 120 flashes without pausing, then around 70, this just doesn't seem to relate to what i expected to be getting (4 digit code)

anyone give me some direction or make sense of what i'm getting, can upload a vid if it helps, thanks,

secondly, are the gadgets available on ebay suitable to plug in and simply get a read out, as that would be easier.