ive never worked on a 94 evap, but my 98 has two, the one that lets the vapor into the TB shouldnt do that until the computer calls for it. it doesnt do that at rest. your canister would be full of gas i would think and you would be getting evap codes if that was the cause of your issues
you could easily check to see if your evap is the cause of your trouble by capping the vacuum line at the tb and see if your issues go away. you would get a ses but it shouldnt affect driveability.
1998 Bonneville SSE
2007 Monte Carlo LT-KYB, Clarion, Polk audio, Kicker
1999 Yukon SLE-KYB, Air lift, Reese dual-cam, Tekonsha
1987 Firebird-355/th400-nothing stock