my 2017 chevy spark dumps fuel down the intake when engine braking down a hill. i presume they do that to keep the catalytic converter warm.
if your car does that, what you may be able to do is wire in a manual kill switch for the injectors.
long term, friend of mine wants to weld on some more metal to the camshafts of 1.9L TDI engines, to keep the intake valve open longer so some of the intake air is blown back out. you then modify the pistons, or the heads, to get the compression ratio back up higher. essentially making an Atkinson cycle diesel engine.
there are many other efficiency improvements to start with before remapping the engine, unless you have a truck and people have already provided better off the shelf solutions. its not nearly as easy as it sounds.
My guess is a misfire on multiple cylinders. Hopefully its just a coil or sparkplug wire. You can disconnect them one by one to identify which one failed.
Buy a 20$ obd2 bluetooth or wifi adapter and look at the data.
usually its rather weak sheet metal so you need to park the car or tie it off to a tree and then use another tree as an anchor point and pull on the metal.
don’t use rope, use a chain, it won’t stretch. a ratchet strap can work, shorten the strap to the minimum needed, but what may work better is a chain binder from harbor freight. you don’t want to pull the metal more than you need to, and a real stiff chain is a lot better than a rope.