Like the title says, it will not start with the vac line hooked up to the map sensor. It started losing power gradualy over the course of a week or so then refused to start one morning. So far I have replaced the cap and rotor, plugs n wires, and fuel filter. I am getting a good spray pattern out of the injectors. I don't know what I was thinking but I pulled the vac line off the map and it fired up, but has a hard time revving, so I replaced the map thinking I found the problem but it's still there. I am not getting any codes except for a map code after I unplugged it. I checked the timing while it was running w/o the map and its correct. I'm at a loss here, HELP!!! (Edit: It's a 91 Blazer 4.3 TBI with 98,000 miles, auto,4X4, A/C)

 

its possible you purchased a faulty map sensor..get another one(under warranty) check the vacuum line and make sure your plug in connection is good, possibly a bent prong