2002 Saturn L300 Tachometer dropping

Hi my Check engine light and service light come on and as soon as they do the tachometer drops down to zero. it has done this while sitting at a red light and while driving 60 to 70 mph. The car does not seem to feel any different and the light comes on for one to two seconds and goes off when the lights come on the rpm goes down when the lights go off the rpm goes back to normal. i went from 2500 rpm to about 100 or 0 and nothing felt different. please help me....... Had two diagnostics run on my car and no codes came up