Aliza, The Lambda unit, is told by the 02 sensor and the lambda sensor to run richer till the 02 sensor heats up and the thermo switch opens. Takes about 2 1/2 minutes on the average. Then after it heats up the frequency valve will alternate on and off as the 02 sensor tell the lambda to adjust it. ( Normal ) John Hervey 11004 dherv10@xxxx