Well, could be but I've had them both for about 2 years. The Ford Moose Pipe Resonator tube fix gets rid of the moose (mostly) but does nothing for the slow rpm change. I did the plug fix to get the rpms to not hang. Also, some times I found when it was really hot out that with just the Ford pipe fix, it would still hum a little at a different speed than before though not as loud. With both in, no moose at all and no hanging rpms either! I had no startup or idle issues for about 8 months or so with this combo, so the system might be more sensitive to idle with both in the system, but I don't think it is root cause. Something else is acting up that is different now than before. Could this be electrical related? I read once about an alternator change for flickering headlights? I don't think I have that problem but it has always been daylight when I've been starting it. I haven't done the alternator mod. Battery is a DieHard about 4 years old now.
I could try taking out the drilled plug and see if it matters - may do that next...
