When the car is warmed up and running a bit and I get on the gas and then let off and coast (not in gear) the idle does not want to hold and dips and dies.

But only when warmed up and after a high rev/boost run.

Vac is reading fine though. And this just started in the last few days.

I have noticed a lot lower than normal voltage readings as well. Sometimes dipping down to 11.1 or so volts.

Any thoughts??

 

I would start with the TPS. It's not hard to check and Clark Garage has a write up that makes it easy to do.

 

Try disabling the ISV at the diagnostic port on the drivers side of the engine bay. Here's how to do that:
http://www.clarks-garage.com/shop-manual/fuel-08.htm
If that doesn't work, I have a TPS that I just used once for testing. I had the same problem last year, went ahead and bought the TPS and it turned out to be the ISV.