Anyone know what fault code 53 is on a '97 maybe '98 (irish plate) Impreza turbo?

It's definitely code 53. The car has an AFM fault (code 23) which flashes once, then flashes code 53 twice before bringing code 23 back up.

 

fuel pump and fuel circuit i think?

 

I don't think code 53 is anything serious, but code 23 is definitely the AFM.

The symptom is the car starts and runs fine for approximately 20 seconds, then dies.
If you run the car with the AFM disconnected, it runs of a fashion (as you would expect i.e. default map or limp mode or whatever), but doesn't cut out. As soon as you reconnect the AFM, the car dies.

 

i have a list that says in general Subaru fault code 53 is to do with fueling

 

According to my PSI3 Hand book Code 23 = Mass Air Flow Sensor,

Code 53 = IMM Control Module EEPROM
EGI Control Module EEPROM
Use of Unregistered Key
Key Communication Failure
Reference Code Incompatibility
Antenna
IMM Circuit Failure (Except Antenna Circuit)
Communication Error (Time Over)

 

Sounds like it could be an immobiliser issue as per above post. The car has an aftermarket immobiliser and not the factory fit version on it.

If it was a fuelling related issue, the car wouldn't run, but it does... providing the AFM is disconnected.

What year of car does your list relate to?

 

would assume 96 on with OBDii

 

yep had a 53 fault code myself took it to prosport they told me it was a immobilser error said it might be my chip in the actaul key that could be failing, since it was my only key i had to get a new key cut and reprogrammed just in case! cost me total of about £100 for a key and diagnostic, but since ive only had the fault code come up once and it has never came up since