I have read all the threads on the speedometer being a percentage off (both on my R55 and R53), however I have now experienced twice my tach now reading high.

Tach should be simple math, engine speed, through transmission drives the tires, all fixed numbers. I can see if my clutch was slipping, it would fluctuate. It does not, randomly it will read about 300-400RPM too high..

When I am going home on the highway, I have the cruise control set at 70, every time. Its typically 2900-3000. Last night for the second time it held steady at 3400 RPM.

My OBDII scanner said it was running at 2900-3000.

This morning on the way in, it read correct.

Anyone ever have this happen?

 

Ha, I've been troubleshooting a high idle. Maybe I just have a high tachometer.

Thanks, I'll let you know,
Peter

 

My tach reads about 200 RPM high. My mechanic was troubleshooting a random CEL light and was plugged into the OBDII while driving it and found the discrepancy that way.