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I read through your other postings. I would want to check codes again to see if you have any new ones. Could be an injector, coil, spark plug wire that is causing the backfire I don't think the fuel filter would play a factor at slow speeds, but with the mileage you have it would hurt to change it. Might be worth spending some time with the original tuner to see if something has cheanged with the cal to be causing the issue.
No, you cannot touch the sensor physically, or lets say you shouldn't touch it. Spray it off with electrical parts cleaner. If the sensor goes bad, the engine probably won't run worth a darn. The MAF calculates how much air is passing into the intake. It does this by heating the element inside of it, the air flow cools it down and the amount of voltage needed to keep it at a pre-determined temperature is measured by the PCM, processed through an algorythm which then determines the air/fuel ratio to set based upon the table information inside.