I have a 2007 Mazda 6 2-litre TS with 44,000 on the clock, which has developed an erratic idle speed when first coming onto idle from higher revs. This then smooths out to a constant level and stays ...

Your engine feels calm at a stoplight because a hidden idle system keeps fuel, air, and spark in balance. That quiet stability is not luck, it is the result of sensors, valves, and software working ...