can anyone suggest how to check vaccum leak related to CEL P0171 - too lean bank 1

 

usually caused by a leak in the intake system somewhere between the Mass Air Flow sensor and the cylinder intake valves. Look for a vacuum hose that’s become disconnected or a crack in one of the tubes connected to the turbo

take a look at this thread https://www.scoobynet.com/general-te...-2002-sti.html

 

What other mode are you running/spec.
What year model etc.

I had that code once and after chafing bits and bobs was related to dv delete and the MAF getting confused so to speak.