If the check engine light came on there is a code(s) set in the computor. You need to have the code(s) read. Many of the auto parts stores will provide that service if you buy the parts needed for repairs from them.
It is possible that the engine is running roughly because of a clogged fuel filter. Many times, that will not register a diagnostic code.
If the engine stops running when the key is released, then the ignition switch is probably bad. The switch will need to be replaced.
Check the engine thermostat.
The engine blows. Usually pistons shoot into the engine. In most cases the engine will have to be replaced.
It turned out to be the alternator going bad. Replaced alternator. No more growling.
Because it's in park.
because you broke it!!
Never disconnect a battery while an engine is running!
Because it is burning fuel in its cylinders.
= "Do you have to flash the computer after you replaced the engine?" =
Yes, because your engine is on.
Check alternator output with a voltmeter A fully charged battery should read approx. 12.8 volts without engine running Should read approx. 13.8-14.2 with engine running