Poor gas mileage on 1999 Volkswagen Cabrio

Replaced wires,plugs,cap and rotor
IGet 16.4 mpg from 24mpg

Asked by for the 1999 Volkswagen Cabrio
Volkswagen parts or aftermarket?
You dont check the ffilter , u just replace , there cheaps.
1 more answer , 1 more comment
Try the air + fuel filter ..
How do you check the fuel filter?