Greeting all,

New user here and obviously new Isuzu owner. I just bought an Isuzu Wizard (or Rodeo as known in the Us market). the car is in Cyprus but came from the Japanese market so its a right hand drive. Its a 2000 model fitted with a 3.0 Diesel (commonrail) engine with 255,000km on the clock with automatic transmission.
When I first got the car there was a tube that was not fitted on what I have found out to be the O2 sensor. the car was put on the diagnostic with no faults being read. I discovered the tube was not fitted on the sensor so when I fitted it the 'check engine' sign came up and the car would just turn off on its own while moving.
I have now changed that sensor and everything seems to be working fine. The only problem is that there is a terible vibration coming from the engine when I change from D in transmission to either N or P. The same happens when you rev the engine sharply. When the revs fall they go lower than the idling (which I consider also a bit too high - 800rpm when idle) and the abruptly up again. It feels like the engine is about to turn off and then goes back to normal. I was told that was caused by the O2 sensor but now that I have changed it, it still does the same thing. Any suggestions?

Also (this might seem a slightly stupid question) but what is and what does it do this button on the photo? I have searched the internet and still have no clue since I have not seen it elsewhere! I am reffering to the middle button with the engine display.

thank you