Rough start/running/stalling issue. Tests to run to diagnose it?

Right now it's back to first principles, which is getting a fuel pressure reading so I can eliminate fuel pumps as an issue. Then I'll worry about MAFs.

As I've said in previous posts my fuel pressure gauge will NOT fit on the schrader valve on the fuel rail. My pressure gauge fitting attaches just fine to the schrader valve in the tire stems, but not on the fuel rail schrader valve, so it appears there are two different sizes for the schrader valve on these cars. What gives? Can someone answer this?

Also, I'm getting conflicting information about whether one should be able to read fuel pressure when the key is in the "II" position but when the engine is not started. Some say yes, others say the fuel gauge will read fuel pressure only after the engine is started. What's correct? Thx

ketel