The tach on my SL never quite stays in one spot. I don't feel a miss, and know that I need to hook up an external tach to know for sure what's going on. Just curious, are these things known to "float" at highway speeds? For those of you who may be having a miss problem, I spent a long time running mine down. Items replaced without helping were the fuel pump and filter, all eight injectors, ignition points and plugs, trigger points, plug wires and distributer cap, and vacuum hoses. Rather expensive trial and error, but I figured these items could use replacing anyhow (except the fuel pump...that was a must when I went in the garage and found gasoline all over the floor). Still, after all this, the miss was as bad as ever. Finally checked the pressure to the injectors. It was all over the place. Replaced the pressure regulator and it purrs now. Still wondering about the tach though. That little float of about 300 RPMs bothers me.