Possible VSS Defective but ...
 

1990 MX-6 Non-Turbo (most importantly - the wifes car):

Suddenly high idle 2K plus and a up and down idle as if a vacuum leak, (isn't) and it's intermittent. Runs dandy when it's running like that and when it's not.

Pulled the code (six quick uninterrupted flashes) and it complains it's the VSS. If so, why is it running fine and can I ignore it? OR establish more proof that, THAT is what it is?

I'm asking this - have read some of the other pots, as I've not found one near this year/model.