Noise when decelerating around 2500 RPM

[jroach]

My 2007 997S makes a faint ticking or fluttering noise when decelerating. Taking it in to the dealer but I love to use these forums as a second opinion.

The noise only occurs when the car is warmed up for awhile and decelerating at around 2500 RPM. I have found that I need to get it above 3500 RPM and let it

come back down to 2500 to recreate the noise. The noise goes away around 2k RPM. Sounds like a ticking or the fluttering of a valve. Maybe exhaust leak but

the car is not that old with around 20k miles. Can only hear it when the windows are up. Makes no difference if the AC is on or off. Any thoughts?

[White987S]

Do you have any mods?

Do you have PSE (Porsche Sport Exhaust)?

[jroach]

no mods and no PSE.

[jroach]

Update: Dealer spent a few hours on the car on Friday. They can hear the noise but can't find the cause.

[White987S]

This is a long-shot, and may NOT apply, but have them look at the 987 TSB# 1726. I know yours is a 997. The early 987's had a "noise" issue at about 2,500 RPM and was related to a faulty oil pump control piston. The repair was pretty easy.

Yours may still be exhaust related. Did they say anything about the cats or mufflers?

[jroach]

I mentioned to Rusnak about the Cats/Muffler but neither of us could think of why it would be both temp and RPM related. My thought was something changes in the heat and the vibration is always there at 2500rpm...you just hear it now because it's changed. I'm not certain I have an oil pump like the 987 but I will mention it anyway.

[jroach]

Rusnak just called and said it was an aftermarket intake. I bought the car used (about 4k miles) from a dealer and the original owner (my opinion) didn't look like the type of guy that would know how to raise the hood. When I look under the hood I don't see anything that doesn't look stock. Can anybody shed some light on what 'aftermarket intake' means? I will stop by and have them show me later but wanted to get prepared.

[355bhp]

Rusnak just called and said it was an aftermarket intake. I bought the car used (about 4k miles) from a dealer and the original owner (my opinion) didn't look like the type of guy that would know how to raise the hood. When I look under the hood I don't see anything that doesn't look stock. Can anybody shed some light on what 'aftermarket intake' means? I will stop by and have them show me later but wanted to get prepared.

Don't know what an aftermarket intake looks like, but here's a topic that has drawings of what a stock one looks like: http://www.renntech.org/forums/index.php?showtopic=8459. I'm sure a search will pull up topics with photos. Good luck.

[jroach]

Thnks. Based on the diagram then my intake box is stock. I suspect they are talking about the filter.

[355bhp]

Thnks. Based on the diagram then my intake box is stock. I suspect they are talking about the filter.

If you live close by to Rusnak, ask one of the guys in the parts dept to point out the aftermarket intake. I've got a rattle in my muffler, but I think it's a loose baffle. I only hear it when I blip the throttle at lower RPM's. However, I think it contributes nicely to the nasty roar it makes when I really put my foot down!

Edited July 20, 2009 by 355bhp

[White987S]

That's why I asked early on if you had any mods. I realize you were not aware until recently about the airbox. Hopefully an OEM part will fix you up.

[jroach]

Thanks 355bhp. I did have Bill at Rusnak show me the part. It's the intake plenum. The previous owner must have added it to the car. I don't think I would have purchased the car if I knew it had been modified but it only had 3900 miles and met all the other criteria I had. Dealer sold it to me and represented it as having the factory warranty....with the modification it doesn't really have a complete factory warranty. I'll likely replace it with factory unit.

The plenum was from IPD/Mike's Performance. I'm heading to the IPD now to have them take a look...I noticed the area code was the same as mine and they are only 20 minutes away. The part that is causing the problem is a loose hose tht comes off the plenum and returns back to the air box. The hose is loose and the back pressure must be making the noise I'm hearing.

more to come.

White987s - I did not know there were any mods.

[jroach]

IPD took a look at the car. He replaced the plenum and the problem has gone away. When installing the plenum he noticed that the hose from the airbox to the throttle body might have been incorrectly seated on the TB. I suspect that this might have been the problem from the beginning but hard to tell now. It was nice to have somebody stand behind their product (IPD) and take the time to help diagnose (at absolutely no cost). It's one mod I would now recommend.

[george996]

without hearing the noise i think it is valves switching from large lift to small lift position. that would explain why you need to rev the engine over about 3,200 rpm for them to switch to large lift. if you have durametric software you can test the valve lift solenoid valve and try to duplicate the sound. playing around with durametric i can make my 04 996 make a similar sound.

Pages_from_2002_996_Carrera_Technik.pdf

Edited July 21, 2009 by george996

[jroach]

Thanks george996 for the idea. It turned out to be a vacuum leak.

[george996]

Thanks george996 for the idea. It turned out to be a vacuum leak.

a vacuum leak is a lot better to have than a valve lift problem. do you know specificaly where the leak was? i would like to know. regards, george

[jroach]

Leak was at the smaller hose that comes from the air box up to the plenum. It clips on to the side of the plenum and has an O-ring. I think just replacing the O-ring the noise would have gone away. I was told that the plenum pressure around 2500 RPM's is at its highest.

[500]

Leak was at the smaller hose that comes from the air box up to the plenum. It clips on to the side of the plenum and has an O-ring. I think just replacing the O-ring the noise would have gone away. I was told that the plenum pressure around 2500 RPM's is at its highest.

Thanks for posting this. My 07 997S just had a new engine installed due to as bad pioston and I started noticing a rattle/flutter etc only upon deacceleration too...I will check to see if this fitment is secure etc and also have the dealer check it out. Could you post a copy of the work order as this gives these fixes from the internet the credibilty the dealer/techs look for. Thanks again.

[jroach]

In summary the work order from the dealer stated:

Description Bin Amount

------------------- ------- ---------

Distributor tube Test $95.66

The dealer did not fix it....they just identified the area (and that was ok). Mike at IPD diagnosed it the rest of the

way and fixed it (no charge). I'm not certain what the o-ring cost would be but I would think less than $10.

[500]

In summary the work order from the dealer stated:

Description Bin Amount

------------------- ------- ---------

Distributor tube Test $95.66

The dealer did not fix it....they just identified the area (and that was ok). Mike at IPD diagnosed it the rest of the

way and fixed it (no charge). I'm not certain what the o-ring cost would be but I would think less than $10.

Went back and read the entire thread...am I correct saying that the noise was was due to the IPD part being installed in the first place?

Thanks

[jroach]

Mike replaced the IPD part and O-ring at the same time. I can't be 100% certain but I would say it was the O-ring. Since the O-ring is so much cheaper I would start there.

The IPD part is aluminum (stock is plastic) so I don't see how the IPD fitting could lose its shape. It might be that when the IPD part was originally installed or when the dealer has done

work in that area that they didn't replace the O-ring.

[500]

Mike replaced the IPD part and O-ring at the same time. I can't be 100% certain but I would say it was the O-ring. Since the O-ring is so much cheaper I would start there.

The IPD part is aluminum (stock is plastic) so I don't see how the IPD fitting could lose its shape. It might be that when the IPD part was originally installed or when the dealer has done

work in that area that they didn't replace the O-ring.

thnx