The flow of Air entering the cabin will be blocked as the filter gets dirty. If you do not want to change it just remove the old filter and leave it that way. No harm will be done. You will just not have filtered air any longer.
change a pollen filter
theres a filter called the pollen filter under the passenger side compartment,google it for more info.
how do you change the pollen filter and which way up does it go on a MERCEDES VITO 2.2CDI 2000 MODEL
There is no pollen filter on any sunbird the oldest GM product to get one is a 1993 Cadillac
HONDA PILOT .ORG - Changing out the cabin (dust/pollen) filter HONDA PILOT .ORG - Changing out the cabin (dust/pollen) filter
GOOD LUCK
You do not list the year. Unless you are talking about a Fiesta built in Europe that is fairly new, it does not have a Cabin Filter. The smell you are smelling is more than likely mold or mildew growing inside the vents. Very hard to remove. Search Google with the term "Odor from dash vents" for advice on how to remove it.
4 parking sensors on the back
It doesn't have one.
Shogun disease/SLE?
Purchase a Purolator Cabin Filter. It comes with detailed instructions.
Purchase a Purolator Cabin Filter. They come with complete instructions.