My 00 neon stall when idling, if I disconnect a vaccum line the idle raises and the stall dissapear. I disconnect the vaccum line that goes behind the fuse box when testing it. I also notice that when I turn off the car it backfires out the throttle body. It only does it when I turn the car off. The car has new wires, spark plugs, fuel pump and regulator, cam and crank sensors, temperature sensor, oil and filter, water pump and timing belt, new drivebelts, air filter, valve steam seals and the upstream and downstream O2 sensors.

 

Does it start hard?

 

When I start it, starts at the second try, looks like the fuel line is empty when I start it for the first time. once it start the first time it start at the first attempt.

 

Leaky injector possibly?