signal to detect remote start engaged?

Which is all very well Ted but doesn't solve the problem any more than my solution, we're still ASSUMING the engine is running rather than KNOWING it's running. There's a chance I could give a definite answer if our poster had the common sense/read the rules and told us make model and year of car. The correct answer would probably be to take tach with some kind of sample and hold circuitry/process control but don't ask me to design it, that's for the Piersons and Oldsparks.