I went through this with my 94 5-speed. My code 543 was accompanied by a code 137, rich left O2 sensor. I replaced both O2 sensors, injectors, resealed the intercooler pipes, replaced every sensor in the engine bay, plugs, wires couldnt solve it. I found the thread that David just posted, checked the vacuum line, no luck. Checked all the vacuum lines, replaced them, pulled vacuum on them individually, pressurized the intake, no luck. I had found a couple of threads that suggested 543 was a problem with the fuel pump itself, but my problem was rich , not lean. If Davids link does not help I would suggest dropping the fuel tank, and pressurizing the vacuum line from the tank to the connection at the fire wall, ruling out damage from rust or road debris. I believe that vacuum line is steel from the front of the rocker all the way to the tank. But if your starving for fuel, it may just be that you fuel pump is on the fritz.