RPM display for TDI engine

Hello,

I installed a TRW speedometer in my Ibiza because the original one showed over 300,000 km. Now I'm having a problem: it's not displaying the RPM correctly. I wasn't aware that this could happen. If you use the 'hidden' menu, the correct RPM is displayed. Does anyone have any idea what might be causing this???

It's a TDI instrument cluster, so it's not a gasoline engine issue! The mileage, MFA (Multi Function Display), everything else is the same, and everything else is working fine! The idle speed is 920 rpm, but the display shows 750 rpm. At 3000 rpm, the display shows approximately 2300 rpm?!

Best, Boro.

After checking everything and installing different data sets on my speedometer, the tachometer works correctly with some, but always shows a lower RPM with others. It seems that different hexadecimal numbers are used for the calculation depending on the data set. Unfortunately, the devices that operate at the correct speed do not have the MFA function, so I cannot use it.

'So, is it possible to manipulate the signal sent to the instrument cluster in a way that it displays the correct value? Would adding a resistor be too much? But what do I do if the signal is too low?' Does anyone have any ideas?