I have a 2010 Ford Edge SEL FWD 3.5L with about 80k miles on it.
It has been increasingly developing a noise that took me a while to pinpoint as to where it was coming from. When in the car the noise sounded like a fan spinning up or a very rapid rattle/knock some where from under the center dash area. I did some digging and narrowed the noise down to the intake manifold area. This noise is not present at start up and idle hot or cold. It only starts when accelerating and most pronounced between 1500 and 2000 RPM. I can reproduce it easily and hold it when I accelerate to that range. When listening at the engine the noise sounds like valves tapping or backfire into intake manifold or something rattling in the intake. I was thinking that maybe the timing is off and I'm getting a backfire into the intake.
What I tried so far:
1. Replaced spark plugs with new OEM plugs. No change.
2. Replaced spark plug coils with new (aftermarket). No change.
3. Replaced MAF sensor with new OEM. No change.
4. Sprayed (Drenched) almost everywhere with carb cleaner to try find a vacuum leak. The idea was if there is a leak the engine rpm would change slightly as it sucks in carb cleaner. Made no impact.
5. Removed upper intake manifold including throttle body, air box and MAF and tried running the engine. Engine wouldn't run until I hooked up electrical connector to the throttle body. The idea here was to see if the issue is mechanical (bad valves, etc). Other than trying to maintain smooth idle without throttle body and MAF, the engine seems to run fine.
6. Started putting the intake parts back one by one and seeing if I can reproduce the noise. With upper intake manifold installed, throttle body installed, vacuum tubes hooked up but MAF sensor not yet installed I couldn't reproduce the noise. When I installed the MAF sensor then I could reproduce the noise. Weird. I'm using a brand new MAF so why is it without the MAF it runs fine but with MAF it makes that noise??
7. I'm lost.
