gt500blue

Hi, I'm new here, but not new to my A8. I also have vag and there are no throttle body codes. I did the procedure to calibrate, but did not help. My car is experiencing this same exact issue as the video shows below. It is repeatable when I give the pedal a quick rev to a couple thousand RPM and on the way back down, the throttle makes this fluttering action. I was hearing a flapping sound and started to look around the forum. I found this video although I have not taken mine apart yet to see it vibrate like this, the sound is exactly the same. I used my mechanics stethoscope and it's definitely coming from the throttle valve. Does anyone have an idea if I need to simply replace it or could this be caused by some other electronic or vacuum related issue?

Thank you!

Quote:
Originally Posted by roxbury51
Audi A6 2005 3.2 L Quattro
On this video, I hear strange noise from the throttle area. This is after I changed the engine valve cover gasket due to leak. On assembly, I broke and repaired vacuum hose. I also took the time to clean the throttle body. I put it back together and had the vagcom throttle adaptation. No codes registering.

The car hesitates and jerks on acceleration and highway speeds. I suspected a vacuum leak but I don't see or notice any. Do I need a new Throttle body which is very expensive or any part like MAF. I do have a Vagcom on hand. Im open to any opinion thanks

Automotive_Buff

My only suggestion before you start tearing it down is to check your intake lines. My A8 exhibited the same issue but on a more violent scale, to the point where it would stall and konk out; also, no codes were thrown up. Follow your intake line from the air box all the way to the block. On my engine, the Indy mechanic had tried to adjust the intake arm after he had secured the air box in; with some force he got it to align and was able to tighten the ring around the neck near the MAF sensor. In doing so, he had pinched the elbow the of the intake system near the driver's side firewall and as a result, pulled the intake out of the block.

So remove your top engine cover, and check the lines there once you've insured the lines near the air box are secure. The elbow has a rather finicky resting spot and is a hard line that won't bend. So if you need to adjust something, loosen everything up from the air box upwards.


I hope this simple suggestion is your issue. If not, then using VCDS measure the air flow. The program will tell you what is the acceptable range.

gt500blue

Thank you! I will check the lines. They all look good. Since I change my oil and air filter, I know I'm the last one to mess with the intake tubes and such. They seem fine after a quick glance in the garage now. Interestingly, I'm getting a MAF code that says it's faulty. I'm going to clean it tomorrow and if code persists, replace it. But I don't think the MAF can make the throttle valve vibrate that hard. It seems like the valve itself is getting faulty electrical current signals and it's opening and closing very quickly but only an 1/8 of in inch or so. I can hear it clicking at a high speed with my stethoscope. To the unaided ear, it sounds like a flapper of sorts, but that is probably the sound of the valve (butterfly looking part of the unit) closing and opening a bit and the noise echos in the hard tube. I think......

Automotive_Buff

I concur the MAF would not make your engine react the way it does. However according the ECU there is a vacuum leak somewhere; that could just be a consequence of your valve improperly operating.

I just want you to make sure it's not some silly/easy fix before you start unbuttoning the car. However, I think your presumption might be correct. In that case I hope it's maybe a sensor issue, or low voltage issue. If not, then a rebuild or a replace might be necessary.

dvs_dave

gt500blue

Dave,
I will be doing this today and report back. It makes sense that if my MAF is truly faulty that it could cause several problems. Great idea.

GT

gt500blue

Well.. good idea, but not the fix. It still does it. I should also say that it does not continuously do it, but it flutters, stops, fultters, stops, etc. No real rhythm to it either. After engine warms up, it does it much less. However, when I rev the throttle and let the RPM drop back down, it does it just about every time until it gets back down to idle. Then it does not do it (once warm). So it's very frequent (like every 8 seconds upon cold start up) and flutters for about 1.5 seconds... Then stops again for another 8 or 10 secs. Then does it again, etc.

I'm thinking that today I will start to gain access to the throttle valve and search for any obvious issues on the rear of the engine (loose piping, hose etc.). I have found them for $50 used on Ebay. I'll probably end up throwing a new MAF and Throttle Valve at this issue since that will be less than $100 or so and see if that works.

But in the meantime, if there are more ideas to share, I'm all ears.

Thanks again!
GT

MP4.2+6.0

For OP, the video you attach suggests it is a 3.2. Is that correct? (Yes, I see video tag is for an A6) I ask because if so, that is a non North America motor for D3's so most of us would not have direct practical experience. More generally, always try to include your motor, year and general location. Each element helps us understand context and likely configuration.

If the 3.2, FWIW I think of it among all Audi motors as sort of the ground zero of carbon fouling. Very early FSI. Convoluted internal ports in the cylinder heads too that can clog and might throw the O2 sensors off and get into a loop with the MAF adjustments. Regardless of motor, that area fits dvs dave's idea of unplugging the MAF, which then has the motor fall back to the open loop operating mode. If it does help or it resolves, then recognize it could be something different than MAF. You should post up the MAF code here though; without it I would not recognize whether the MAF is actually the cause, or if it is just feeding into some other issue.

For a few other ideas (besides valve fouling), if the 3.2 uses an intake flap system like the 4.2, make sure the mechanicals of that are in order. No broken linkage, so broken vacuum components, that is moves, and so on. If 4.2, of course check all that directly since we know that motor has the intake flap set up that is proving somewhat problematic as these get old.

For throttle body, it uses sweep type electrical contacts internally. Those can wear and create issues, including ones I could imagine could tie to yours. I might expect a code though. They can usually be opened and the contacts (carefully) re-bent to increase spring pressure, along with cleaning the swept contact surfaces. Obviously buying a cheap junkyard one also gives you a practical swap out test for it.

Farther afield things could be an issue with the suck valve (aka suck pump aka vacuum booster or vacuum booster valve--inline Y or T plastic piece in the big vacuum line that drives the vacuum booster on the power brakes), or in the power brake booster itself. I don't recall any posts on the latter, but the former has been an occasional fail area back to C5's and D2's. The one on my W12 (T instead of Y shaped) outright broke open when I was putting part of my intake back together and created a huge and thus obvious vacuum leak.

gt500blue

Thank you for your help! I realized I did not put the specifics in the post.

I will grab the Vag-Com report log and upload next. I'm having several different issues at the same time which may or may not be related. But your thought about the T or Y and vacuum lines is interesting. I have a code that says my antilock brake module is faulty as well. I have one that I'm going to replace this weekend. But I will upload the full report next.

FWIW, the car is a 2005 A8 D3 so the 4.2L.

Thank you!
GT

MP4.2+6.0

On ABS, the fault is usually with the electronic module (if your code simply says "defective"). Way easier to just change the module than to deal with the whole ABS unit and the nightmare of getting it completely bled with the brake line hook up complexity. Module is screwed to the side of the ABS unit--where the wire harness connects. Folks often just send them out for rebuilding--now available for D3 ones I think. Often as simple as a cracked solder joint internally that develops over the years with under hood hot and cold cycling.