More than likely what is happening is you have an intake valve sticking open when it gets cold. Once the engine gets warmed up the carbon and gunk on the valves gets less sticky and the valves will close normally. If the valve is sticking open the compression from the cylinder it is feeding will go out through the valve and into the intake manifold. This is the reason your vacuum hoses are blowing off it is to much pressure to hold them on. The backfiring that you are hearing is the spark plug detonating the fuel and traveling up into the intake. You will need to have a good valve decarbonizing done to correct this. Most of the stuff you buy in the parts stores is not going to do it. The best thing to do is go to your local GM dealership and have them do a good cleaning on it. They have a very good injector cleaning solvent that cleans the valves very well. You may also have a weak valve spring that is not allowing it to close fully.
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