78montecarlo

I had a chance to drive another 2006 Audi A4 quattro with the 2.0T and 6spd auto. I had driven one wih a manual before, and while I noticed it was noisy, I don't remember it vibrating much. Maybe a little at idle, but once running it was ok. However, the car I drove last night with the automatic transmission vibrated quite bad at idle, especially under load (sitting at a stop light) and worst when cold. Once reved off idle though, it was smooth as can be. The idle was so bad I thought something was wrong with the car. My 138,000 mile pushrod 3.1L V6 runs 100X smoother at idle. The Audi person excused it and blamed it on the turbo (guy did not seem very smart). That did not satiate my curiosity, so I went online to research. Apparently, all the A4 2.0T auto trans cars do this idle vibration. Its worse when cold and worse under load, which implicates all automatic cars are most prone in gear at a stop. But apparently, any other car with a 2.0T is nice and smooth (Rabbit, Jetta, Passat, A3) all the time. People on the forums were baffled how the more expensive A4 can vibrate so bad at idle and the same engine in a cheaper VW GTI can be so smooth at idle.

My question to you guys is, do Direct Injection engines tend to have poorer NVH, causing the rumble in the A4? Some special control loop they enter at idle where it goes really lean and just barely supports combustion? Or is it something specific to the longitudinal engine placement and quattro on the A4 that causes the vibes? Again, all the transverse applications of the same engine seem to be smooth? I tried to find the root cause on audiworld.com, audizine.com, foutitude.com and lots of people noted the problem, but none could explain why the A4 2.0T does this. Even some smaller auto publications that test automatic A4 2.0Ts notice it. The big mags like Car and Driver, R&T never notice becuase they always test the manual trans car. The solution on the forums was to either buy a manual trans car so the engine never idles under load when stopped (in neutral or clutch is in), or shift the auto into neutral at stoplights.

Does the new direct injection CTS V6 do this? To compare 4 cylinders, do the direct injection turbo Solstice engines do this? It seems some manufacturers have a handle on the NVH, like the IS350 V6. Is it the unbalanced nature of the 4 cyl 2.0T that exaggerates the vibration, so a DI 6 cyl would be ok?

I can see this came up before. But the GM engines were too new for anyone to have experienced. Any new information since then?
https://www.camaroz28.com/forums/sho...tion+vibration

Z284ever

The 3.6 is just not very smooth at idle in general. There have been lots of complaints about it from CTS owners for years, but with no real fix. The DI 3.6 also clatters alittle at idle as do most direct injection engines, but you don't really hear it once you're moving

routesixtysixer

My 2004 A4 GTO had a terrible vibration under load at idle, but only when outside temps were 60+. It was really irritating. Like a big magic fingers bed. As outside temps approached 100 degrees, it was so bad that the dash actually hummed and buzzed. All you had to do was lightly put your foot on the accelerator pedal and it smoothed right out. I tried bumping up the idle speed with a hand-held tuner, but that just made it hard to drive (loading the converter, etc.). I even changed a motor mount (on my own dime) in my attempts to rectify. Never could get rid of it, so I got rid of the car (which I loved otherwise). Don't know if there is any correlation (probably not) but reading this post reminded me. OTOH, the 06 CTS 3.6 I had seemed to idle fine.

Threxx

Yep lots of direct injection motors get complaints for being rougher and louder, especially at idle and when cold... it's really pretty similar to the high injection pressure of a diesel engine and the similar engine behavior that it causes.

I had an 06 Audi A4 2.0t w/ 6-speed manual and I didn't notice any vibration (I guess since I didn't have the CVT (auto?) that you say has the issue) but it was definitely a noisy motor... had a diesel-ish racket to it, especially when cold and idling. I noticed this from day one since my previous car was a Lexus GS400 and the motor on that car was the most smooth and inaudible motor of any car I've owned by car.

I'm convinced that good engineering can make most of that go away. Go drive a Lexus GS350 and you'd never know it's a DI motor unless maybe you opened the hood and listened to it from outside the car when it first started up.

jg95z28

My stepson hasn't complained about the problem in his '07 A4. I'll ask him when we next chat about cars.

Eric Bryant

The Lexus V6 has a set of indirect port injectors to go along with its direct-injection system.

Threxx

I guess I'll pretend like I understand the implications of that statement.

78montecarlo

No this was a 2.0T quattro with a 6 speed tiptronic automatic. A traditional automatic with a torque converter. Not the CVT or the DSG they use in the transverse engine applications. And its not just noisy, but you can feel vibrations. I could tolerate a coarse sound, the ticking at idle,etc. But this vibration made it feel like it was only firing on 3 of 4 cylinders. I figured it had to be a crappy example, but the web forums imply they all (A4 2.0T quattro w/ tiptronic) do this... Threxx, I think you did not notice the vibration as I believe you had the 6 speed. So at idle, the only load on your engine to exagerate the vibration would be electrical and the ac system. Your clutch would either be in or you would be in neutral. No load from the torque converter which seemed to aggravate the issue on the car I drove.

I was kinda bummed to notice this. I had alwasy thought highly of the 2.0T for delivering decent power and such nice fuel economy, even on the AWD configurations. Like I said, I dont know if it is the engine, or if it is something specific to the longitudinal engine placement with the torsen quattro set up. The 2.0T in the Passat/Jetta/GTI/A3 don't vibrate. I was considering a used A4 2.0T quattro with manual but this bugs me. It may not be as bad with the manual, btu will it get worse as the car ages and eventually become noticeable?

routesixtysixer

FTIW, my 335i (DI 3.0 I6 w/ZF 6-speed auto) is a little noisy on cold start, but quiets down after just a moment or two. This is only a "sound" quality though (not feel) as the straight six is very smooth idling. Threxx has one, as well, so he should be able to validate the BMW DI six idle quality.

HAZ-Matt

Just a dumb guess but it sounds like what my car would do when the idle tuning was not dialed in properly. If the idle airflow calcs are wrong you end up with the wrong amount of air and fuel and the spark moves all over the place to keep the idle stable... and you get nice vibrations.

Eric Bryant

Sorry for being too brief On the Lexus V6, the "indirect port injectors" (which is a fancy name for what the vast majority of modern vehicles use for injection) are partially responsible for fuel delivery at idle and part-throttle. Only under certain conditions does the direct-injection system provide 100% of the fuel. This, in effect, is the best of both worlds - it's just kinda expensive! Consider it an evolutionary step.

Threxx

So it's a direct injection system that's supplemented by a traditional fuel injection system and some sort of fancy transition takes place depending on throttle position? Hmm... what are the benefits of that? Just quieter and smoother at idle or something else as well like even better fuel economy or power? I thought DI was superior in all ways to standard fuel injection which would mean they're only doing that to make the motor more luxurious while still maintaining most (or all?) of the benefits of DI?

Eric Bryant

Yep, that's exactly what it is. You can see both injectors here:



Both injectors are located in the upper left of my photo - the direct injector is located under the intake port and points directly into the cylinder, while the indirect port injector is located in the intake port (sorta half in the intake manifold and half in the head).

Direct injection systems can't atomize the fuel as well at low engine speeds, so the port injector is used to shoot some fuel at the back of a closed intake valve. When the valve opens, the inrush of air past the valve does a good job of atomizing the fuel (this is exactly how sequential systems have operated for well over a decade). At high loads and low engine speeds, the amount of fuel provided by the direct injector might be in the range of 40-60%, with the port injector picking up the rest of the task.

Also, during cold starts, the Lexus engine uses a combination of injection to minimize emissions - the port injector gets things going with a bit of well-atomized fuel, and then the direct injector gives it another shot once the burn has initiated. The overall mixture ends up being slightly lean overall but is actually a bit rich in the immediate area of combustion - it's a rather novel compromise between homogenized and stratified mixture.

At WOT, the engine switches to 100% direct injection, as this minimizes pre-ignition and thus allows maximum torque output.

Don't buy into the "DI is superior" hype just yet - it definitely helps in some areas of engine operation, but is inferior in others. Keep in mind that the world's best spark ignition racing engines still use indirect injection (hell, some of the highest specific-output engines use carbs), and that a lot of manufacturers who could afford direct injection aren't currently using it. Piezo injectors for DI are supposedly on the way, and that might help make up for some of the shortcomings by allowing for multiple injection events per combustion cycle. Eventually, it'll prove itself superior to indirect injection, but like any new complex powertrain technology, it'll take a while to develop DI to its full potential.

Todd80Z28

To me, this is a pretty common phenomenon with transverse mounted four cylinders. Virtually all the larger 4 cylinder cars I've driven do this to some degree at idle. The Acura TSX with the 2.4l 4cyl I had on loan put a significant amount of vibration into the body at idle- you could feel it in the seat, steering wheel, etc.

My 2.2l '95 Accord EX wasn't too bad, but it had a sizable counterbalance shaft, and some flimsy motor mounts, so alot of the vibration got absorbed. How's the counterbalance on the Audi?

78montecarlo

Thats the goofy thing though. Because of the Torsen Quattro set up, the A4 has a longitudinal engine arrangement, like the S2000. But according to most, the transverse engine arrangements from VW/Audi(Jetta/GTI/A3/Passat) are the smooth ones. Its this longitudinal A4 with the vibes.

The 2.0T does have dual balance shafts, but they apparently are not enough for the A4.

http://media.vw.com/article_display.cfm?article_id=9755

Interesting article that describes Audi/VW method of implementing DI. Kinda stinks they apprently have 3 modes of operation for Europe that allows very lean burn. But our crappy fuel here prohibits this feature on North American cars. The article makes it sound like they did try to quell the vibrations and funny noises with flapper vales and other features. I wonder if that is the cause of the vibes on the A4? THey designed it to work well with European fuel, and they had to compromise their design to work with the US fuels? Resulting in ticking slightly rough DI engines for those in the US? Maybe that is why Lexus uses the second injector as they were trying to design around our fuel in the first place?

I know this isn't muscle car news, but I found it interesting