Tachometer Check

Attach an external high quality tachometer to the engine speed detection connector on the harness side (such as with a paper clip).

Fig 1: Attaching High Quality Tachometer To Engine Speed Detection Connector On Harness Side
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.

NOTE: For tachometer check, use an external high quality inductive tachometer.
Compare the readings of the vehicle tachometer and the external tachometer at every engine speed, and check if the variations are within the standard values.
Standard value:

Fig 2: Engine Speed Specification
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.