When starting 1997 A4 Audi Quattro, it starts for 3 sec and then stalls, the immobilizer light on dash is on. I have used both keys locked and unlocked the car many times. How can I get it started?

You make it sound like it's our fault you can't find it :>D

The start of production of the Audi A4 B5 is 1994. With minor changes, it was produced until 2001. At first, only the sedan version was available, the station wagon (Avant) appeared a year later. This material provides information on relay circuits and fuses Audi A4 b5 1994, 1995, 1996, 1997, 1998, 1999, 2000, with an assignment of their elements and locations.

Can't get much clearer than this. Relay 4 is one plus 'Additional Relays 23 and 24. Plus fuse 23 and 24.

Fuse box diagram Audi A4 B5 and relay with assignment ...

https://fuseandrelay.com > audi > a4-b5

This material provides information on relay circuits and fuses Audi A4 b5 1994, 1995, 1996, 1997, 1998, 1999, 2000, with an assignment of their elements and ...
‎Passenger compartment · ‎Main fuse box · ‎Relay box · ‎Engine compartment

Could be a bad ignition circuit (from the ignition cycinder)

if your main computer is under your drivers seat it may be wet. that will start affecting all kinds of electrical

Tow the car to the dealer ship. they can reset this usually fairly quickly and it is not worth the headache to try and deal with yourself. It sounds to me like your key has lost its programming and the car will not start until it is reset.

does the check engine light come on or flash when the running issue starts? sounds like you have an ignition coil dropping out intermittenly.

Not sure about Audis but it sounds like the security system has fuel injectors restricted and if so thats a dealership job to replace the BCM.

It's the light bulb for the car electronic immobilizer.

463A definitely not VAG codes they are from one of the cheap code readers.
Audi A4 Quattro - fault code 463a: engine control unit disabled.
This could be a dirty sensor or bad connection somewhere.
The immobilizer light flashes when you insert the key?
Imobiliser pick up loop in the steering column sounds dodgy, take the cowling off & check its connected ok. Just clipped it back in.

immobilizer not recognizing key. vehicle will start and cut out immediately. try unplugging instrument cluster and recconecting as they sometimes develope a bad connection due to connector pins being very fine. check connection between ignition barrel and dash cluster. immobilizer built into cluster. if engine control unit has been changed immobilizer won't recognise it, must be adapted using diagnostic reader. this is done by entering instruments [code 17] select adaption [code 10] and channel 00 [erase learned values] and confirm. keys may need to be adapted to immobilizer [only at dealer as key code is needed.

Hi I'm litoshop before you continue trying to turn on the car check the timing belt if the car stalled while driving and you have more then 70,000 miles most likely the timing belt is gone and if that's so then check you did not bent the valves good luck if this information has been helpful please let use know thank you