I had a persistent problem with pinging/detonation under WOT in 5th gear on the highway. I tried the usual cures - ran two bottles of injector cleaner through, cleaned the MAF sensor, etc. - no change (although the car did run better after the cleaner). Finally, I went to our fairly reputable local Ford dealer. I found out that despite my cleaning efforts, the MAF was still contaminated and would have to be replaced. While this could have just been due to age (I have 74k miles), I had just re-oiled my K&N prior to taking the car in, so to avoid risking further damage to a new mass air sensor, I had them re-install my old stock paper-filter induction system along with the new mass air meter. The car runs fine now. Without the K&N the car does appear ever so slightly less perky, and the fuel mileage is the same from what I can tell. In other words, no real noticeable difference although I am sure I lost some high-rpm power (K&N claims up to 10 hp at high rpm for the FIPK).
I think that this dealership is pretty reputable, because they didn't make a big deal about my K&N, although when I asked my service associate, he said that could be part of the contamination problem. This filter had never been oiled except from the factory, which perhaps explain why it went 35,000 miles without a real issue.
Bottom line is I learned that for day-in, day-out maximum reliability for a car that serves as your main transportation, the stock parts do pretty well. I had 35,000 miles with the K&N, and maybe I'll put it back on someday, but the tradeoff in driveability was worth my removing it for now. I don't usually drive the car to the max, so the ever-so-slight performance loss is not a big deal.
I think that this dealership is pretty reputable, because they didn't make a big deal about my K&N, although when I asked my service associate, he said that could be part of the contamination problem. This filter had never been oiled except from the factory, which perhaps explain why it went 35,000 miles without a real issue.
Bottom line is I learned that for day-in, day-out maximum reliability for a car that serves as your main transportation, the stock parts do pretty well. I had 35,000 miles with the K&N, and maybe I'll put it back on someday, but the tradeoff in driveability was worth my removing it for now. I don't usually drive the car to the max, so the ever-so-slight performance loss is not a big deal.