Abstract: Method of reducing noxious or toxic exhaust emissions from an internal combustion engine (10) having a plurality of cylinders (12) cooperating with a crankshaft (13) to cause the crankshaft to rotate at a rotational speed when the cylinders (12) are provided with an air/fuel mixture having a lambda value and the mixture is ignited to generate pressure in the cylinders. The method includes measuring a parameter reflecting the pressure in a first cylinder during at least a part of a working stroke of the first cylinder when supplied with an air/fuel mixture having a first lambda value to thereby obtain a first parametric value. An air/fuel mixture is provided to a second cylinder, which air/fuel mixture has a second lambda value which is different to the first lambda value, to cause the second cylinder to perform a working stroke. A parameter is measured reflecting the pressure in the second cylinder during at least a part of the working stroke of the second cylinder to obtain a second parametric value.