Volvo 440 Error codes

Does anyone know how I can get the stored error codes from the
diognostic test point of my Volvo 440. The ECU is a seimans type and
the fuel system is a B16F. The car has been idling roughly over the
past 9 months. While cold the idling is quite rough. After this the
idling speed settles at about 1000RPM. This is set by the constant
idling system. However, when the throttle is pumped the revs fall to
about 600RPM before picking up to 1000RPM. It has recently been cutting
out. When this happens, it will not restart until at least an hour
later. There may be a temperature issue and I'd like to see if the
error codes will give me any clues.

Maurice.