Originally Posted by Ducthess

It doesnt really feel like surging...the only thing that I am feeling when I drove the car was that everytime I came to a stop it would stall (it is an automatic) if my foot wasn't on the pedal giving it gas and revving it, and it didnt seem to want to shift...I don't know how to really explain it. When I had half the header done (it was clamped to the cat and the O2 sensor was just placed on the bung) I pulled it out of the garaged and just slammed the gas, it drove fine then, had a lot of power and such...maybe that blew the line off...but I dont see what would cause all the driving and stalling problems.

Originally Posted by mazdaspeed7

A vacuum leak will certainly cause that on FC's. The MAF meters the air coming into the engine, and the computer determines how much fuel is needed based on the airflow. A vacuum leak is basically unmetered air getting into the engine, so the ecu isnt adding enough fuel. Lean mixtures result in misfires, stumbling, and stalling at low rpm. And yes, one vacuum line is enough to make the car stall when you let off the gas and let the engine fall to idle.