Hi guys.
I have a 2008 F-150 STX with the 4.6L Triton. During very light acceleration....I mean just gently resting your foot on the pedal I get this hissing sound from the left front of the engine compartment. It will go away if you accelerate more aggressively. When the cruise control is activated you will also hear it during subtle throttle changes. It sound like rushing air or vacuum. I think it is just noise coming from my air cleaner. My Miata has an aftermarket intake and it makes a similar sound. Does what I described sound normal?
Thanks!!
Dom

 

It probably has a Cobra engine in it
Sorry about the bad joke, It just Sunday morning.
Maybe someone has an answer for you!

 

Maybe the idle air controller bleeding off

 

Good one

Probably just a vac leak. Can you hear it while stationary/hood open/accelerating using the trigger under the hood?

Almost sounds like the EGR pipe. Maybe the noise quites once the valves open.

You can purchase a vac tool @ Auto Zone and test the vacuum harness and all lines.

WAIT! It's an 08 - Just take it in ..Warrenty ..

 

I would go for the warenty, and they will shrug you off. Make them give you an analisys in writing and keep up with it. If there is a problem it will show more in time.

Keep all records. I've learned that from my wife. She was a cost analist for Lockheed. She now works with me. She has helped me maintain a proffit margin even in tough times.

Sometimes it is hard to work together tho!

But do check all vaccum lines. jbrew will laugh at this but: Check the line going to the EGR vaccum regulator mount at about the 10 O;clock possition beside the brake booster and trace those lines out.
it could also be just air going by the throtle plate.
It's probably a normal sound.

 

Thanks for the info I'll check those lines.
Dom