You could try spraying the racks (empty, of course) with one of those super shower cleaners that you spray on and it dissolves the soap scum. Spray well and close the dishwasher. Let it sit for awhile, then run the dishwasher (empty, again) using a packet of lemonade Kool-aid or Tang. I wouldn't add any vinegar just yet because it might react to the cleaner.
If you don't want to use the cleaner, heat some vinegar and spray the racks with the warm vinegar. Then let sit and run the wash again with the lemon kool-aid or Tang.
Good luck. :)