I have been having the grinding lately. Thought it was my brakes since they were the original set and I had 144,xxx miles. Replaced pads, rotors, and parking brake, issue still remained. Narrowed it down to the IWEs. Disconnected the vacuum solenoid and noise went away, but fuel mileage had been dropping significantly. Replaced plugs as well since I assumed they were the original set as well, but no change. Plugged back in the solenoid just for grins and grinding returned. Put a vacuum gauge on the engine side of the check valve and had 25 in mmhg. Put it on the vacuum lines that go directly to the IWEs and it held at 25, so IWEs check out fine. Broke down the rubber line between the check valve and solenoid and checked it with the vacuum pump. Turned out to be a leak in the angled rubber fitting on the bottom of the solenoid, the one with the double mail nipple. Replaced the check valve line set (fl34-7a788-ad). Grinding went away and fuel mileage increased.

 

Surprised to hear MPG hit was that bad. I capped off my system as a preventative measure to avoid failing IWEs. What do you estimate the hit at?

I average ~16MPG in my '15 5.0.

 

I was babying it and only got ~14.5 city/highway, and that was after replacing the plugs. Now I'm at upper 16 not really trying.