audi a3 1.9tdi immobilizer problem

hi all,new to this so thanks in advance for any help.

my problem is as follows-
sometimes my a3(2005) wont start(immobilizer) and i have to disconnect battery lead for a second to reset system and hey presto starts no problem.it can work fine for a few weeks and then act up every 3th or 4th time i try start car.
it has become annoying now and need it sorted as its a pain having to lift bonnet on main street or as today a petrol station.

also my outdoor temperature guage reads -14 even when its 20degrees outside ??????
anybody ever had this problem or any advice?? thanks

regards eoin

any help from anybody?????

hi all.
thanks for replys- im in wexford,ireland.
if i dont do the disconnect battery fix car wouldnt start and would be stuck at station.dont want to bring it to a "clock immobilizer repair" place if its only something easy to fix????