In Peugeot 207, an unstable idle state may be associated with a catalyst warmed up. As long as it does not reach the operating temperature (about 250-350 ° C), the cylinders may be enriched or, in contrast, depleted, depending on a number of other conditions. In response, the ECU shall adjust the engine speed. After the catalyst is warm, the oxygen sensor passes the correct data, the mixture is stabilized and the idle speed is normal.
