why would it no be
Misfiring on a petrol injection engine is caused due to incorrect ignition timing. As the engine rotates, the timing determines when each piston fires or ignites.
When the engine is cold or when it is misfiring.
Check your engine timing, it may be too slow.
Engine cylinders # 1 and # 4 are misfiring
Timing belt. misfiring engine
The number 5 engine cylinder is misfiring
The P0300 code indicates random engine misfiring. The P0303 and P0304 codes indicate the cylinder #s where excessive misfiring is occuring.
Bad plugs/coil/wiring
by sensing engine RPM it can teel if engine is not running smooth by sensing the rotation of the rpm's of the engine.
The catalytic converter
It could be (a) misfiring cylinder(s). Check the condition of your plugs and wires. Also, check if your engine mounts are not worn.
An engine computer does not cause a misfire but merely reports it. The misfire is probably caused by the ignition coil or plug wires