OBD 2 codes need help

[ndrake]

I have a 96 Jetta GLS with a 2.0 manual trans with the code p0501 coming up the speedo will work than not work and then work and not work cant exactly figure out why. does anyone know if this is a electric speedo and therefore need to replace a sensor or value or if this is a manual speedo and need to replace cable and gear. Also the car has three other codes p0171 p0510 p0440 and if anyone else knows what these codes can mean please let me know. I have to get this card smogged and it will fail for sure and i really dont want to have to pay to get it fixed by dealer or independent shop right now. Also if anyone knows the location of these sensors as well as the canister purge valve that would be lovely as well

thanks
Nick