I am looking at GIAC chips right now, how do I know which chip to get?
From the GIAC website:

1996 - 1999 B5 A4® 1.8T 8D0906557M 91- 93 octane performance
1996 - 1999 B5 A4® 1.8T 8D0906557P 91- 93 octane performance
1996 - 1999 B5 A4® 1.8T 8D0906557N 91- 93 octane performance
1996 - 1999 B5 A4® 1.8T 8D0906559C 91- 93 octane performance
1996 - 1999 B5 A4® 1.8T 8D0907559 91- 93 octane performance

Also I am not sure if I have a 1999 or 1999.5... how would I find out and does it matter?

 

Look at your ecu number and match it to the one provided by giac.

 

ok thanks guess im really dumb

 

haha nah its cool.

 

and to tell if your car is a 99 or 99.5 the 99.5 has one piece headlights the newer tails and the vin will have the last digits that are over 200000