My wife has a cowoker who has a 99 Maxima. The car will shut off when she is coming to a stop. Doesn't happen all the time.
A garage said it may be the map sensor and quoted her $500.00 to replace it.

Any thoughts what may be the problem?

Yes, MAP Sensors are expensive, but $500 is ridiculous. Only replace the MAP Sensor as a last resort.

Get a scanner and check for any codes being thrown. Autozone will do this for free. If it indicates the MAP Sensor is the problem, shop on line for the best price (e.g. RockAuto.com) and replace it yourself. They are normally super easy to replace.

I would also make sure her idle speed is set properly and that normal ignition maintenance has been performed recently; e.g. spark plugs. Most V6 owners neglect replacing plugs, because of the difficulty of reaching the rear plugs. Platinum plugs should normally be replaced at half the recommended mileage. My hunch is that this could solve her problem.

Thanks tx. What would a ball park price on the part be?

Which part?

Here's what a MAP Sensor would cost:

http://www.rockauto.com/catalog/x,carcode,1356780,parttype,5124,partGroup,19

Look at the associated picture. How difficult does that look to replace?

Looks very labor intensive to replace. LOL
Thanks for the info.