Chevrolet Repair: rough engine at start, chevy impala, test port

Question
hi i have a 2000 chevy impala with the 3400 engine i seem to have deveioped a problem that no one can seem to figure out when i start the car in the morning or after its been sitting for about an hour the car runs good for the first minute then it starts to shake and the motor stalls if it does not stall and i proceed to take off it seems to boggle and lose power . but the problem goes away completely after about five minutes i have been to the repaire shop and have had the plugs checed and they were good they hooked up the computer on it and it showes that there is nothing wrong with the car there is no check engine light coming on . what else can this be.

Answer
Hi Mike,
That sounds similar to a problem I have had on some diesel engines I have.
Due to a tiny leak in an "O"ring, the fuel drains back out of the system, back into the tank, and draws a slug of air into the line.
When you start it up, the fuel that is on the engine side of the air bubble allows the engine to run correctly, but then the air gets there and causes the problem. The problem corrects itself as the intank fuel pump continues to operate, and pushes the air on through the engine, and also through the fuel return line to the tank.
A pressure tester connected to the fuel system and observed during the problem would help, but it needs to be left on overnight, or at least through several sit cycles.
If the air is getting in through the pressure test port, though, connecting the tester might temporarily correct the problem.
Make surt that test port has a cap screwed on tightly.
An experiment that might help....when you have let the car sit till you know it will have the problem, instead of cranking the engine, hust turn the key to run for about three seconds, then off, then to run for about three seconds, etc. several times. This will run the fuel pump through its prime cycle, and should push any air through and back to the tank. After several key cycles, see if it eliminated, or greatly reduced the problem for that start cycle.
If it does, that would verify my suggestion.
Good luck, and let me know how it comes out.Van