There are a couple methods for car carpets, this is a cost effective thorough process here:
1) Shop vac thoroughly
2) clean interior:
dust by using your blower on the shop vac to blow out the crevasses, Mild Meguiars APC protectant with a moist microfiber cloth clean glass etc. apply your preferred protectant
3) re-vac if needed for new soil and churned up soil from your above the carpet detailing
4) Folex sprayed by spray bottle or bug/weed sprayer and worked into carpet with a moist brush, get carpet damp but not wet then let it work a few minutes. Empty dust etc. and filter from shop vac and extract. Respray stains with Folex, Woolite dilute etc. and brush then extract.
Harsh stains will require more treatment. Prochem etc. professional carpet cleaing mfr.s make good stain removers, see their web site for your local dealer.
5) Rinse with clean water sprayed and brushed in and after emptying the 1st soiled water in the shop vac keep rinsing until the water in your vac is clear.
Do not over wet.
You can use the Bissel or Mytee makes an excellent and well priced extractor detailer for car cleaning with heat. Heated water is your friend when cleaning your carpet and seats.
6) I prefer brushed carpet when damp to bring up the nap but I do strip the carpet too.
7) Let car dry in sun or use fans.
8) Use Scotchguard if appropriate. Carpet cleaning distributors have the large bottle for 40.00 or less that lasts forever, use a bug/weed sprayer to apply the diluted mix to carpets and seats.
ROAD SALT use vinegar to break it down, don't grind it or just use water as it won't get out the material well. It will smell like sulfur, extract and rinse then clean as above. It will be completely removed with vinegar, diluted or full strength as patience and time dictate.