If you're already renting a steam or water extraction carpet cleaner for your home once a year or so you should also use the cleaner on your cloth car seats and floor mats rather than chemical upholstery cleaners.
We previously covered a tip from household weblog Hostess with the Motzes on how to save money by using vinegar in rented carpet cleaning machines instead of branded commercial products -- the author of that weblog also shared how she used a 50/50 solution of white vinegar and water with a few drops of lavendar essential oil in the rented Rug Doctor cleaner to clean years of accumulated spills and mud in the upholstery of her Honda minivan.
The prevailing wisdom to keep cloth seats and carpeted floor mats clean is to never eat while in the car or walk in muddy areas and if you happen to do so make sure you immediately clean the stain. This advice doesn't work for many busy people these days, especially if you have small children. So if you periodically rent one of these machines to give your home carpet a once-over consider doing the same to your automobile upholstery.
Using the Rug Doctor and Vinegar in Your Car's Interior [Hostess with the Motzes]