camd01silv

I have a friend with a 98 Camaro with a pair of 58mm turbos on it. He got it dyno tuned a while back when the car had a stock cube ls1 in it, aftermarket heads, pretty aggressive cam, and a fast 102 tb and manifold. He blew up the ls1 and bought a bone stock 5.3 for the car. Now whenever he starts it up, it will idle high for a couple seconds and then die. If you give it gas, you can keep it running for however long you want, but when it tries to return to idle speed it dies. He doesn't have the coin to go get it retuned and I have hp tuners... I can fix it if it's nothing major. I just don't know what it could be. Any ideas?