W210 A/C Actual Values #21
 

My 99 E300 actual value #21 is 42 at cold start idle (ambient temp 74F) in park.

My chart says #21 is engine speed and that rpm's are counted in 100's.

My tach needle shows my idle is ~675/700rpm which feels correct (although maybe a tad low).

Is my chart wrong or is the sensor that value #21 is connected to at fault?

I confirm that on my '96 E300, #21 is the engine RPM in hundreds. It shows 6 at idle, with the instrument panel tach showing 650-700.

However, I don't think that the N22 has a separate tach input. I'm pretty sure that the instrument panel and the N22 tachs are fed by the same sensors, but I don't recall which feeds which. Perhaps the signal goes to the N22 over the serial interface on my car, along with the ECT (#6). Yours is newer so it's probably a bit different, but I still doubt the presence of multiple sensors.

Thanks for checking yours Matt L.

Can anyone confirm if value #21's scale is different for a 99 vs 96, or if mine is providing erroneous info what I do to repair?