I have a 1991 subaru legacy which dies our after i start it?

the computer tell me that its the surge selenoid from the gas tank so I put it direct and it worked fine for five minutes and then it started dying out on me again. when the engine is in low idle it will stop but if I press the gas pedal to the bottom it will reb up to 5000 rpm without a miss if I keep it between 3000 and 5000 rpms it will run without a miss otherwise the engine stops. But sometimes I start it and it will run without any misses and after a will it will start missing and the engine stops. This car has a plug in the cumputer for checking the engine codes. When I connect the plug and turn the key to on position the cooling fan on the radiator starts to go on and off, and the relays will start to click on and off, also the gas pump will turn on and off. It's as if I was tuning the key to the on and off position over and over again. I did test the purge selenoid by connecting a test lamp to the battery and no current goes thru it.. my next step is to bring a computer and plug it to the car ecm to see if it will give me another code. anybody got any ideas as to what it could be.