Hi.. 2 questions.. I have a 1999 Audi A4 1.8T quattro

1.) got a P0501 check engine code and speedo doesnt move and gas gauge is irratic. RPM guage works fine. So I replaced the VSS and am still coming up with the same code. Trying to get the vehicle inspected but no go till the speedometer works.. any suggestions.

2.) does anyone have detailed instructions on how to replace the factory head unit after taking out an aftermarket. or wiring instructions.

any help would be greatly appreciated.
cyn~