when I am driving mycar thr RPM will go all the wasy over and the enginelight comes on … then my car will kinda stall but when I shut my car off it goes back to normal then it happens again but there is nothing wrong witht he transsmissionit is working fine please help .
That description doesn’t really contain enough information to get you anywhere (though on the face it, it surely doesn’t sound good).
Post the make/model/year/mileage of the car. Give some idea of how well its been maintained, and what has been done already (if anything). Have the codes (from the engine light) read and post those. And provide a bit better description - is this every day? only when car is hot? Only at high speed? etc.
Anyway you slice it, you need to get it to a mechanic. It may only be something simple, or, it could be more complicated.
It sounds to me like you might have a bad rectifier on the alternator or voltage regulator.
The tachometer goes all the way over? Which way, up or down? If down, I’d guess you are losing ignition, since many tachs use ignition pulses as a source. This would also explain the engine stalling. I’d be looking at primary ignition circuit.