It has been pointed out to me that I unfortunately got a little sloppy in the way I wrote this posting resulting in an inaccuracy in the description of the mixture surging. When the engine is stone cold, the lamda ECU runs the car in a fixed mixture mode and does not use the input from the lambda sensor to regulate the mixture (via the signal to the frequency valve). The period where the car runs in this fixed mixture mode is for the first minute or two after which the exhaust gasses should have warmed up the lambda sensor. For the remaining period of the engine warmup (once the fixed-mixture phase is over) the lambda ECU handles the regulation of the mixture and it is this phase that the oscillating mixture likely has an impact on idle quality. I apologize for my sloppiness in not clarifying that the mixture oscillation I described only applies during engine warmup after the very initial stone-cold period (a couple minutes) is over. Knut