Engine will idle but shuts off when in gear and you press the accelerator?

The vehicle lost RPMs and fell on its face when merging onto the interstate. The engine didn't shut off or throw any codes. It still runs while in park and will move at idle but wants to shut off if you push the accelerator. A transmission shop has already said it's an engine problem and not the transmission. They said it is probably a bad sensor somewhere. Again, there are no codes (Snap-on code reader). I think it could be a throttle position sensor but without any codes I am somewhat at a loss. I am not a mechanic but know a few things. With all the sensors it "could be" I need some help.