It shouldn't matter what position the MAP is in, but there is a way for you to test it while its on the car. But first, I would check to see if there is any dirt in the connector, or the male/female metal terminals aren't quite touching each other (this happened on my trunk release motor). Also check to see if the MAP vac tubing is in good shape. If all that looks good, grab a multimeter. According to my manual, you will need to put the negative probe on the black (or signal ground) wire of the sensor, and you will have to probe the other wires for a 5 volt reference (ignition on, engine not running). If you have a vaccum pump, put it on the sensor. @0 in-Hg, it should read 4.6-4.8V, @5 in-Hg, around 3.75V, 20 in-Hg and it says its around 1 volt.
Hope this helps
Welcome, downwardly mobile yuppies, to the dawn of the Age of Nefarious.
1993 SSEi - FrankenJinx - dead and gone.
1994 SSE (136K strong) - 180* t-stat,HD alternator, most unequipped SSE on the club, XM radio, Kenwood CD/MP3.
2006 Chevy Malibu Maxx LTZ - Custom 2.25" manifold-back exhaust w/FM-80. Probably the only Maxx with this system.