Car shuts off when idling, makes loud noise from exhaust when pressing on gas

So today we stopped at a red light and the car turned itself off. We put it in neutral, and as long as we pressed the gas it would stay running and move, but then a loud noise that sounded like we were revving the engine at high speeds came from the exhaust. It was higher pitched than the normal exhaust sound, in fact it almost sounded like a cow in distress. As soon as we stopped pressing on the gas it would shut off again, no check engine light. There was a smell, kind of sweet but not like a coolant smell. We just had work done on the car, the guy patched 3 major leaks in the intake tubes. We also have a catted downpipe we just put in, a new intercooler, and replaced the exhaust. Any ideas as to what is going on please?