Anyone Know Any Bad Info On the 1.9L TD AAZ motor(goodorbad)

[QuickTD]

With the tach being RPM driven, does this affect the reading?

 The tach may fall a little slower when revving in neutral, as the alternator freewheels, but there is no difference when underway.

[James8485]

can jsut any garage do a compresion test on it as the compression is so high??? also if someone has alterd fuel is there any way to get it back to stock without haveing to take it off the car and have it re-calibrated?
the last part is off topic but it was just on the top of my mind