Anyone care to explain the essential and non-essential devices on an impreza- non turbo (mine being EJ18E 1994).

For example the MAF - if I disconnect the car will stall.
Ignition off and restart -engine runs fine.

This should now be put into a backup mapping as the ECU did not pick it up on ignition-now that it is out .

Using this example which of the devices which are being sensed by the ECU are critical and which are only there to perhaps improve fuel economy or power .

Or if you have any links to read up more on this quiery.

Thanks
Bradley