On a carb when the throttle is slammed open nothing happens outside of the accel pump shot until air velocity through the carbs throttle bores increases. Still playing with it.

Fitech 426 Hemi First Start Youtube
Fitech backfire through throttle body. There is more fuel and less air. Fitech fuel injection does not represent or warrant that the functions contained in the site will be uninterrupted or error free that the defects will be corrected or that this site or the server that makes the site available are free of. Not a real issue but it does catch me off guard at times. Vw volkswagen bug bus ghia thing all. Look at the fitech system and all the wires duration. My guess is the tps was telling the computer the throttle was closed giving the engine very little fuel causing it to go lean and backfire randomly when driving.
To get engine to start you may have to press the throttle pedal slightly. Thinking my timing might be a wee bit off. All wires are in proper sequence. The ratio of air to fuel in the mixture gets skewed in favour of fuel ie. This is why a steady throttle foot is necessary for best efi fuel economy. This locks the ecu in idle.
Ls style 4 bolt intake manifold aluminum throttle body housing with cable drive 92mm single blade. If the engine wont stay running without keeping your foot on the pedal a little turn the throttle adjustment screw clockwise another half turn. Once engine is running and at operating temperature turn on idle set mode. I still have an issue with a very slight hesitation but its sooo much better than the carb. Engine is popping thru throttle body starting at 2000rpm. Man is that a sneaky problem or what.
I had a backfire through the throttle body the other day. Backfiring through the exhaust is a result of problems arising out of rich fuel mixture and out of turn sparking of spark plugs. I too have experienced a stiff throttle. If any body else is having this problem check the tps sensor and give it throttle when the engine is running. Although there are many problems that can cause the intake system to backfire the overall effect is the same. Since the intake valve needs to provide the engine with a proper balance of fuel and air a backfire occurs when that balance fails.
Cause of backfiring backfiring is a small explosion.