When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hesitation at 27K-3K RPM - Maybe Solved? Need help
2009 C2S 118K miles..
Ok... calm down... I can't believe I may have found the hesitation problem in my car.... but I need you folks to do an experiment for me.
It appears to be the stupid resonance flap thingy in my airbox. This flap is only on the S models. I believe the default position for this flap is OPEN... when you start the car, the flap closes...... If I am wrong about this, let me know.
So, if you have an S and you experience the hesitation, then please, just unplug that vacuum actuator that is snapped onto the right side of the airbox and see if the problem goes away. Just unplug the electrical plug and not the vaccum lines.
Easy to do: 1) Unsnap the valve from your airbox (tricky, it moved directly rearward, you have to lift the snap in front and push it rearward), then 2) Unplug the electrical line.... twist the unit over on its side, then slide a screwdriver under the metal clamp... the clamp slides straight away... it does not swing... then the plug removes very easily. To get more slack in the line, unclip the cables from a little clip under the tail light. SEE PICS BELOW
You will set an error in your computer... it will not trip a dash light. I can easily reset the computer code with my Durametric, or just have your dealer do it next time they examine your car.
I can feel no performance degradation at all... the car just sounds smoother..... obviously because there is not sound change from the air plenum. I have driven this now for two days... highway, around the little hills that show this off well.... etc etc...... gone. I have since covered the electrical socket and plug with electrical tape to keep the dust out.... I am going to drive it this way for a few weeks to see if I can tell a difference.
So, why am I getting this and other S owners not? Maybe I have a vacuum leak and the pressure is not high enough for a faster transition... or maybe the valve is sticking. If you reach your arm over the air plenum on the top of your engine, you can feel the valve back there... in the middle of the engine attached to the top air plenum... and you can twist it (you are moving the butterfly inside) Mine does not appear to stick.
Other non-S owners also report the hesitation.... I don't know why. I still can feel an ever-so-slight effect at around 3K where I think the variocam is activating.... but it is slight. If my hesitation was say a 10, it is now a 2.
I am driving this car every day since Saturday AM when I unplugged that air valve thingy...... I can say this without doubt, most of the hesitation is gone. There is no doubt in my mind (today at least!!!) this flap is a big cause... but not the only cause.
When the engine is cold and still warming, I drive it and don't rev past 3500..... occasionally I can feel something going on around 2700 or more like 2900 RPM... It is not at all bad.... I summize, that this is the variocam doing its thing. As others have theorized, it is the combination of the flap and variocam activating at the same time that give the feeling of a quick hit of fuel starvation. Once the engine warms up to full hot, I can't really tell anymore.
So.... given I was hearing a "Phsst" when that flap flipped, maybe there is an issue with this system... sticking? vacuum leak or pinched hose? I see the tube part number is superseded by a new one (just and increment). A new part number may mean they fixed it or maybe they are getting it from another supplier..... who knows.
On Sunday, I ran the car pretty hard and frankly I can not tell any performance hit with the flap disconnected... even Porsche literature notes it is for sound.... other information about this flap?
One voice in my head just leave it disconnected 'cause it is fixed, while another competing voice is saying I just knocked off 100 HP...... sheesh.
Anyway, stay tuned, more to come on this.
C'mon, guys, just disconnect the electrical to the little valve thingy and report.... it takes all of three minutes to do.
Peace
Bruce in Philly
From my literature library..... I was in error above where it says just the sound is effected... apparently is does effect torque.... read on...
You know what? Maybe I got Kim Ks undies stuck in there.... clogging the vacuum...?
Last edited by Bruce In Philly; 08-30-2017 at 10:20 PM.
Doesn't hitting the sport mode also open the resonator flap?
I don't have a sport mode.... MT with PASM, no Sport Chrono... so I have a PASM Switch.... that is about it. I thought that only effected the shocks. No? Let me know.
I don't have a sport mode.... MT with PASM, no Sport Chrono... so I have a PASM Switch.... that is about it. I thought that only effected the shocks. No? Let me know.
Peace
Bruce in Philly
Sports mode re-maps the throttle response.
I think what you're experiencing is the vario-cam changing.
Isn't that flap part of the Helmholtz resonator, which requires different lengths for different engine regimes? If so it is not just for sound.... as different lengths affect the intake air charge and therefore performance.
I think I am just going to throw some money at this..... whoohoo!!
I think I am going to replace the tube with the flap, the vacuum gizmo, and maybe that valve thingy. Prior to discovering that I can make most of the hesitation go away by disconnecting the change-over valve, I was seriously thinking about replacing the variocam actuators when I do my plugs in 1500 miles, but that was going to be a hail mary play. Given that I can hear a "Phsst", well... that is all I need to know for a project.
9A1.110.120.12 Distributor Tube (with flap) $74.04 position 11
This is a newer part number than original
993.110.462.02 Vacuum unit $85.41 position 13
996 605 123 01 Change-over valve $36.42 Position 21 & 13 (2nd pic)
I found a used tube with vacuum unit on eBay for $50 total, but the part number suffix was 04. My Katalog denotes the part as 11, and the newest number is 12.
If any of you know how this system works maybe you can explain why there appears to be two change over valves involved... one next to the air box on the right (as stated in that Porsche pub I posted in a earlier post) and one attached to the tube next to the vacuum unit (rear of engine).
The swap looks pretty straight forward... look for instruction on renntech and rennlist for replacement of the 997.2 AOS ... looks pretty easy actually.
So do I just do one piece? all of them? Hmmm
FYI, appears there is no Helmholtz resonator in a 997.2.
Peace
Bruce in Philly
Last edited by Bruce In Philly; 08-31-2017 at 09:14 PM.
I think I am just going to throw some money at this..... whoohoo!!
I think I am going to replace the tube with the flap, the vacuum gizmo, and maybe that valve thingy. Prior to discovering that I can make most of the hesitation go away by disconnecting the change-over valve, I was seriously thinking about replacing the variocam actuators when I do my plugs in 1500 miles, but that was going to be a hail mary play. Given that I can hear a "Phsst", well... that is all I need to know for a project.
9A1.110.120.12 Distributor Tube (with flap) $74.04 position 11
This is a newer part number than original
993.110.462.02 Vacuum unit $85.41 position 13
996 605 123 01 Change-over valve $36.42 Position 21 & 13 (2nd pic)
I found a used tube with vacuum unit on eBay for $50 total, but the part number suffix was 04. My Katalog denotes the part as 11, and the newest number is 12.
If any of you know how this system works maybe you can explain why there appears to be two change over valves involved... one next to the air box on the right (as stated in that Porsche pub I posted in a earlier post) and one attached to the tube next to the vacuum unit (rear of engine).
The swap looks pretty straight forward... look for instruction on renntech and rennlist for replacement of the 997.2 AOS ... looks pretty easy actually.
So do I just do one piece? all of them? Hmmm
FYI, appears there is no Helmholtz resonator in a 997.2.
Peace
Bruce in Philly
I'm now wondering if this is what causes the irritating noise at 2,800 rpm ....
08-27-2017, 05:06 PM
Hesitation at 27K-3K RPM - Maybe Solved? Need help
