AFAIK, there is no official way to clean it. Cleaning solvent is a no-no since that will contaminate the sensor. Some of the pollutants can be burned off but it has to be in a controlled environment - You can't just bake the sensor :-p. Personally, I would suggest leave it alone, unless you are really getting crappy mileage. If that is the case, it may be worth it to buy a new sensor and see if that helps.