I cut off my exhaust and my car wouldn’t start, when it did it idled terribly then stalled but then after I held down the pedal for a bit it doesn’t do it anymore, should I be alarmed, and if so by what I’m thinking a sensor but I cut it off right where it connected to the muffler and as far as I know there isn’t an actual sensor in the muffler

 

Did you cut off one of the catalytic converters you "thought" was a muffler?
They have wires running to them and sensors mounted to them and everything...

 

You engine is controlled by a computer (PCM) which operates in a set field of parameters. When you cut off exhaust to make it loud you create backpressure that is insufficient to be within the range programmed to the PCM. In response, the PCM retards timing. In other words, loud does NOT mean power, it just means loud.