Shut off problem

Sometimes(just started) when i start it will drop and idle real low, .5 or less and shut off. I have to rev it a few times to keep it running but when i toss it into reverse if i dont go right away it will idle low and shut off. THis problem just started a few weeks ago after i got my flowmasters put on.

check you choke, and run a scanner on it, maybe the engine is starving for fuel, and what kind of mod chip do you have??