yes, a backfiring... same as me right now.

All the times I haven't been able to fire up the engine cranking when I quick release the key to OFF I get backfiring.

when I can't fire up the engine while cranking after get that backfire sometimes I have made to start the engine right away OR SOMETIMES when releasing the key to run in an specific moment...

and IS NOT a wiring or power deal, I'm sure about that.

Engine temp affects that too... with hot engine but off for some period is harder to start up.

I can feel also quite often RPM variations while keeping gas pedal steady at certain speed