The rev counter on my 96MY WRX is giving some inconsistent readings. At 3000 rpm the speed in all the gears is correct. At 4000 rpm and up it seems to be reading low (the rev counter that is ). At tickover it is reading high.

Car seems to be running ok. What I would like to know is where does the rev counter pick up the data. Is it a mechanical pick up or an electronic sensor? What are the engine management implications of bad readings from the rev counter?

I haven't had time yet to check the error codes.