is there a way to test if this is faulty?

have just converted to stu's closed loop, but having a few niggles that need ironing out before i can enjoy decent fuel economy.

i tried adjusting the CO the other day and couldnt get it down enough (to 0.9% recomended) so stu suggested it may be a faulty lambda.

before i shell out yet more money buying parts(for the conversion thats sposed to save me money ), can someone tell me how i can test mine to see if its working?

i'm under the impression it hasnt been used since the car was chipped, as the previous chips didnt use it. just wanna make sure its that part, at fault, before i buy one and find it it was working fine

please help