This weekend, I heard for the first time the sound of a flap in the passenger foot well area. It happens when I turn the key toward ignition. Specifically it sounds like a flap that is attempting to open, sticking momentarily, and then slapping open. Can someone give me an idea of what this is / what it does / why it opens on ignition key turn so I can research it a bit more, and figure out what to do?

Thanks
Dave

 

More than likely it's one of the vent flaps for your HVAC. They actuate with vacuum.

I'm not sure why they would actuate on start up, hopefully someone else will chime in.

 

Afshin, thanks. I should add that I don't need to start the car. Just turn it to the active pre ignition spot on the ignition switch.

Dave

 

I'm not sure that the HVAC controls (vauum actuated flaps) commence to operate on ignition on.

However you can prove or disprove this readily.

Leave the car overnight, then get in and press the brake pedal about twenty times - this will get rid of any residual vacuum left in the system (if you are lucky enough to have a 928 that has absoutely no vacuum leaks - fairly unlikely) If the brake pedal then feels like you are trying to press an immoveable object you no longer have vacuum in the system (remember this feeling for when your engine stops but you still need to brake)

Then turn on the ignition - if it still makes the "noises" it's not vacuum related.

 

Yes, the footwell flap closes *I think* (not opens) when turning on the ignition. When it's 'creaking' either the hinges need to be oiled or the vacuum is low - eg. vacuum leak in one of the other actuators.

 

Jon, thanks for the tip on isolating the problems. Will give it a shot.

Much appreciated,
Dave

 

If you have a perfect vacuum system (and we will all envy you if you do), Jon's test won't work, because the little chek valve between the brake booster and your HVAC will continue to hold vacuum in the HVAC.

 

I would say its more of a click / slap than a creak. Sort of like a flap / door getting stuck on something, OR something impeding the motion of the flap. I think that eventually the door / flap forces its motion, and you get what sounds like the slapping sound of a plastic flap. Now if there is actually a something impeding motion or this is a vac system "catching up", or something else is definitely beyond my knowledge in this area :-)

Thanks,
Dave

 

Wally, thanks but I am pretty sure there is no worry of that ! :-) My car seems to have all the typical age related problems as everyone else, so I would say its a pretty good bet there is a leak or two.

Thanks,
Dave

 

If you have a mity vac you can try to reproduce it by removing the drivers side console cover, look for a yellow vacuum line and put the mity vac on it.

 

Sounds good. If I recall, Dwayne had posted a good write up that shows these vac lines.

Dave

 

Dave, I get this same sound in my car!

I've been meaning to post about this for a while now but have had bigger fish to fry. I was going to try to include a sound clip of it, but from your description I am CERTAIN that it is the exact same sound. It sounds like a ventilation-system flap valve slapping closed (or open?). Mine doesn't do it every time I turn the key - maybe 50% of the time? I think that it only happens when the car has been sitting for a bit - not after it's been driven.

I also thought it might be related to the vacuum system, but that didn't make sense - as Jon indicated above - unless an electrically-operated gizmo is activating something vacuum-related when the key is turned to ON. Dunno - it's a mystery.

Anyway, I'll be watching this thread intently! Let me know if there are any checks or tests I can do (I have a Mity-Vac, still in its blister-pack, desperate to be used for something!).

GAZ

 

GAZ,

I'll be happy to post what I try / find, though it can sometimes be a while before I manage to find the time to work on the car. Like you I also have other issues to deal with - ABS light, leaky oil pan, etc., etc. Interesting to note that the car has been sitting for a while, and the sound made its debut right about the same time.

I figured I would undo some of the easy things to get to in the passenger wheel-well to try and get a better idea of where the sound is originating from. I will also do the vac testing since, a Dwayne write up (http://dwaynesgarage.norcal928.org/1...0Procedure.htm) seems to show that it is fairly easy to access the vac lines discussed. Likewise if you come across anything, it would be great to hear it.

Cheers,
Dave

 

Pretty sure it is the recirculation flap opening or closing for some reason.
Behind the glove box and below the blower.

 

Thanks Roger, I was wondering where the recirculation flap lived ! :-) I like the sound of it as a starting point too since it seems relatively accessible and seems to be in the general area of the sound.

Cheers,
Dave