[Fuergrissa]

code P0-171 is for bank 1 running lean. The hose was a vacuum hose but I cant tell you what it was for because I'm not familiar enough with the impala bay to tell what you describe the other end was connected to.

Basically the hose being off or loose allowed the motor to suck in extra air behind the MAF. because this extra air entering the moter was un-metered the ECM doesn't know it's there and cannot compensate for it by adding enough fuel, hence your fuel/air mix was too lean. the O2 sensor in your exhaust sees that it's leaner than it should be and the ECM throws the code and CEL you saw. Running too lean can cause spark knock (detonation) which is very harmfull, so it's good that you remedied the situation!