Weird off-throttle and mid-throttle noise - 986 Forum - The Community for Porsche Boxster & Cayman Owners

wmjosiah · 02-21-2018, 05:03 PM

Hi all,
New here - just picked up an '01S that I'm really loving. I introduced myself in the appropriate forum elsewhere. Hi! Anyway, the car currently only has two issues, which may or may not be the same one. One is a small groan/hum on-throttle from idle coming from the intake. Most noticeable when you're trying to maneuver in a garage and the sound of it bounces off the walls at you every time you just barely touch the throttle. This one I know is from the intake because it's easy to reproduce and I pulled the engine cover and had someone do it while I stuck my head under there. Another, similar noise, which I would describe again as a groany hum, at speed, mid-throttle. This one I'm less sure is coming from the intake, but with the top up and the engine cover off, it's pretty clear. With the top down it sounds like it's coming from the front right air vent. It goes away if you get on or off the throttle. Sometimes it will go for days without doing it - it seems to do it less in cold weather - and then some days it will do it reliably, all day long - like today, which was almost 70 degrees here. It's MUCH louder with the top down. It's always exactly the same pitch, and it has a kindof rattle in it too, as if there were a bad fan bearing and the blades are hitting the edges of the tube it's in or something. I've recorded it - you can just hear it in the background over the road and wind noise in this file: http://insanetechnology.com/weird_boxster_midthrottle_hum.mp3
My first thought after some quick searches is the AOS, but I'm not entirely convinced. Thoughts?
Thanks in advance,
-Josiah

wmjosiah · 02-24-2018, 05:08 AM

No ideas at all on this? Has anyone else ever had something like this happen? Should I get a better recording?

thstone · 02-24-2018, 05:44 AM

Diagnosing a "hum" (or possibly two different "hum's") over the internet is really hard - especially when it only occurs when you increase throttle (which increases the background sound level).

I listened to the recording, but to be honest, its hard for me to pick out the sound of concern. If you can get a clearer recording and include some annotation as to exactly when in the recording the hum occurs, it will give folks a better chance of recognizing it and providing some useful feedback.

wmjosiah · 02-24-2018, 01:02 PM

Thanks, totally understood - will do. Sounds like this isn't one of those "Oh yeah that's really common, it's blah blah blah" so it'll require better recordings. I'll use real recording gear. Thanks.

Geof3 · 02-24-2018, 01:36 PM

The left vent is the intake, the right is the primary cooling fan exit. Could you simply be hearing the fan perhaps? Also, if you haven't already check your air filter. Could be dirty. As mentioned above, nothing really sounds out of sorts in the video.

Rich XTR · 02-25-2018, 08:35 PM

My 2000s had a noise from the vent in the gas cap area. It was easy to find because you could be parked with the car at 2000-2500 rpm and it would make the sound. When driving i thought it was from the fan opening on the passenger side. It was an evaporative emissions valve that went bad. The valve i replaced is in the passenger fender.

wmjosiah · 02-27-2018, 04:57 PM

Hi all,
The mid-throttle noise was definitely from the vent in front of the gas cap - my son and I pinpointed it while driving around with the top down today - Rich XTR called it, though I didn't see this until now. I got a better recording of the noise: http://insanetechnology.com/2018_02_26_17_04_42.mp3
I stuck some wadded-up paper in the vent and the noise is gone. However this noise isn't at idle, just mid-throttle at any RPM, and it goes away if I get on or off throttle. Purge valve, think ye? I wonder if it might take care of the little off-idle squeak which is definitely coming from the intake (I can hear it clearly with the engine cover off) too, recording here: http://insanetechnology.com/2018_02_26_17_09_26.mp3
Thoughts?
Thanks!

wmjosiah · 02-27-2018, 05:05 PM

I guess the question is do I do this the vent line with valve, part # 996-110-129-06-OEM
Or this:
https://www.eeuroparts.com/Parts/79509/EVAP-Purge-Valve-99620114301/?gclid=CjwKCAiAoNTUBRBUEiwAWje2lvzVwPOP-4DD1Dd2hDsnLbbV1gQTirDwOvMG3f8ueQppCD2YnN2YjhoCNWQ QAvD_BwE
Or the Vapor canister purge valve, part # 996-605-201-01-M244
First? Or something else?

wmjosiah · 02-27-2018, 05:49 PM

After reading up on this a bunch more, I came to the conclusion that there are a lot of valves in the system that can get stuck. Hm. Stuck solonoid valves gummed up with who knows what in such a way that causes them to suck air into the intake... OK, let's spray some throttle-body/intake system cleaner in there. Did that, took it for a drive, a bit later, when it usually makes the noise, I could clearly hear it open, suck the liquid into the system, and then... no more noise. I drove around for five more minutes and heard it open one more time, much smaller noise. Stopped, sprayed some more in, drove around for another 10 minutes, no more noise. This may, obviously, not be a permanent fix. We'll see.

Rich XTR · 02-27-2018, 07:51 PM

Hopefully it is fixed for good. But if not the part number that fixed mine was 996-605-213-01.

wmjosiah · 03-02-2018, 02:29 PM

Thanks! We'll see. So far, it's much better - happens less often and is quieter when it does, but it's not totally fixed. I'll probably end up buying one of those.

wmjosiah · 05-28-2019, 06:51 AM

It got worse again and I started getting a P0455 as well (Evap System - large leak), so I bought a 996-605-213-01 and replaced it. Interestingly, the noise did not go away, but the code has not returned. I have driven it about 400 miles since replacing the valve. Previously it would come back within 100 miles after clearing it. I figured the noise and the code were two pieces of the same problem, but perhaps I was wrong.
I tied a thin piece of rag around the fuel filler hinge to keep it from getting sucked into the valve and stuck it in the hole. It doesn't block the pipe nearly entirely... but noise gone. I'd love to fix it right though, if anyone has any other suggestions. While fixing my Porsche with a rag is funny, I might prefer other methods.