lumina starting

96 lumina just had intake mainfold gasket put on now after 500 miles i try to start it and it seems to but immediately stalls when i let go of the key. When it stalls it sounds like a clanking sound as it comes to a stop. If i give it the gas it runs but I smell gas and don't want to make matters worse?????

Crankshaft Position Sensor? Anyone have any other ideas?

Crankshaft Position Sensor? Anyone have any other ideas?
i found the vaccuum hose off the brakes also disconnected and recconnected some sensors now it works. Was it the vaccuum hose? thanks for the help anyway gave me the confidence to try to tackle it myself and it worked

That vacuum hose would definately do that, not the sound, though. It was probably a backfire that popped the hose off. It may do it again, then you may need to find the cause of that. Or not. Glad it's OK now. Good job! It's amazing what just taking a critical look and fiddling a little bit can fix sometimes.

If the vacuum booster was disconnected that would really cause a problem. By the way you were describing it, I might have suspected the security system to have been causing you trouble.