cadillac cts has slight tach flutter
 

So I have been noticing on my 04 cts that on the highway with cruise control on. I notice the tachometer floats ever so slightly. Maybe 100rpm max. I also notice during acceleration somtimes it will float. I am guessing my ground the body is dirty. Where is it located

depends on road
depends on gas
car may pick up speed and slow down according to road and tach are a general look at thing its the main computer u really want to watch your tach may float but in actual computer time there is no difference
so if u have someone who can do a live scan get it done

i have autotap, so i may hook it up. Now that i think about it it started shortly after i put in my k&n air filter. I also took my old mans fusion for a spin and noticed it was moving on cruise. So I think i just had an OCD moment. I also exaggerated on the amount of the float, it was closer to 50rpm