My experience is that the first bottle improves the part-throttle response. Whether it is the carbon or cleaning up the injectors to improve the low-flow-rate pattern, I suspect the injectors but I've never done any kind of test other than just running the stuff.

I've pulled injectors from several cars in my self-indy days, it is very common to see the CIS injectors put out a stream at low output, but when the sensor plate is lifted for more flow, the pattern clears up to a nice atomized mist. A good clean injector should create an atomized mist from the very first pop, even at idle flow rates, and without it you lose power and efficiency. Replacing injectors is what I used to do, it gets tedious and expensive to put them in every 60,000miles or less (when you're as picky as I am about engine NVH issues).

I don't know how much cleaning of the stems it does, once the symptoms go away I just drive them happily. Italian tune-ups and long high-speed runs are the norm for my driving so theoretically a good running engine shouldn't carbon in my cars.

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Gone to the dark side

- Jeff