I have been having horrendous problems over the past couple of days, where my car has been refusing to start. Its a 1997 Audi A4 TDi by the way. I am 99% sure it is an immobiliser fault, as when it won't start with one key, it will start with the spare key. But i have also found out that it's not the key itself that's faulty, as both keys play up. Anyone heard of this problem before, and what is the likely culprit