MAP Sensor Check Valve?
 

There is a one way check valve at the MAP sensor, which I don't under stand. It is designed to read both boost and vacuum...so why the check valve. Secondly, my check valve has flow in it both ways... and it sounds like a pcv when you shake it... Is my check valve bad>? Should it not be there at all? Which way should it aim?

that's not the check valve.it is just a filter.

Its a filter to keep out gas/oil I believe.

I believe the filter is to prevent fuel and oil from making it to the MAF and damaging its inner workings.

Its just a filter. Without it the map sensor will eventually die. A new map sensor is something stupid like $400.

http://www.rx7store.net/product_p/gm3bar.htm

GM3bar MAP sensor for FD = $75

That only works if you already have a standalone ECU.