car will turn over and run for a few seconds and stall

Had the heads rebuilt by a top shop when they were installed now the car will turn over and run for a few seconds and die. the heads were rebuilt 100 percent new gaskets. The car was down about a month. When u try and start it it runs rough for a few seconds and dies. It doesn't run long enough to build compression. It seems like a security problem except it did run for about 2 minutes once. I am a transmission and motor builder bit this is my first Porsche. It is a 99 911 carrera. Any ideas