Abstract: A known control arrangement for a combustion engine, adjusts the air:fuel ratio via a closed control loop using the oxygen content in the exhaust gases as a measurement parameter. However, this control arrangement only adjusts with accuracy to the stoichiometric value of the air:fuel ratio. A novel control arrangement is provided which adjusts and maintains an air:fuel ratio deviating from the said value. For this purpose, two sets of data are stored in a microprocessor system, one of which corresponds to an adjustment to the stoichiometric value and the other of which corresponds to the desired value. The control loop is closed periodically and adjustment to the first value takes place. The correction values found during the aforesaid adjustment are stored and are used again, as the case may be after adaptation, for the adjustment to the desired value.