Mitch105

Hi guys

Anyone else notice that when slowing to a stop the tranny drops the revs a little too low as it comes to a stop for a second causing the engine to stumble/vibrate just for a split second until the revs come a back to regular idle?

I find it annoying and wonder if I should bring car in. Not sure if other engines are doing it.

Thanks

Mitch

irenesbob

Mitch -
Not really. I have a 2013 A6 2.0 Quattro with the Tiptronic. Do you have the Tiptronic or the CVT?
In any event, I think what you describe is more of a tranny issue than an engine problem and may have been addressed on this forum. Overall, I find my 2013 2.0 a far smoother engine than my 2010 3.0 engine was.

Mitch105

It is a tranny issue for sure. So you say the issue is addressed in the forum I'll search then.

You find the 2.0 smoother than the 3.0? Funny I would never assume that.

irenesbob

Yeah, but I might be the only one who feels this way - maybe there was an isue with my 2010 3.0. I had a 2006 and a 2008 A4 both with a 2.0T and neither of them was as smooth idling or non-intrusive as is my 2013 A6.

Jatmobil

No such issues with my 2.0t CVT!
Contrary to popular belief, inline engines are just naturally/mechanically smooth, the inline 6 being the smoothest of them all. Done several vibration analysis on these engines as part of my Kinematics of Machinery class during the undergrad years. It is no coincidence that BMW is heavily vested in inline 6 engines!

Richard Solomon

I'm sorry, did you just claim that an inline 4 cylinder engine is naturally balanced without need for compensatory devices?

Jatmobil

**Warning - Long Post***

Nope! Not at all! On the contrary, I am claiming that when there are even-firing cylinders per bank, the inherent design is smoother (eg. I-4, I-6) where we(engineers) have to deal with only the second order vibrations (not as easily felt or observed by the naked eye) than if there were odd # of cylinders per bank (eg. V-6) where the issue is the first order vibrations or end to end rocking motion, which are more easily felt by humans.

When there are even # of cylinders, there is naturally some counter balancing going on between the cylinders as the intake, compression, ignition and exhaust strokes of cylinders in the front of the engine are somewhat cancelling or opposing the ones in the rear, the I-6 being the best at it as the front half of the engine is the mirror image of the rear half. In the case of the V-6 you have odd # of cylinders in each bank and there is not much naturally available to compensate for the dynamic imbalance that leads to an end-end rocking motion.

Of course, both the inline engines and V engines need counterbalancing measures, where the I-4 can get away with just counter rotating balance shafts, whereas the V6 may need counter weights on the crankshafts in addition to the counter balance shafts as well.

Sans-counterbalancing, odd # of cylinders in a bank would be harsher. What really makes the Audi 3.0 TFSI problematic is the use of a 90 deg bank to accommodate the supercharger. The rule of thumb is that the angular rotation of one complete stroke i.e, 720 degrees divided by the number of cylinders, i.e. 6 should be evenly divisible by the bank angle i.e. 90 degrees for the TFSI so: (720/6) = 120 which is not equally divisible by 90 and therefore needing extra measures of counterbalancing as compared to a Toyota/Lexus 60 degree V6 where 120 is equally divisible by 60!

Nothing beats a boxer engine (any # of cylinders), closely followed by I-6.

B.T.W - the jury is not out on this! This is proven over and over with some quick kinematic/vibration analysis using some basic second order differential equations.

Richard Solomon

Ok, whew I agree. Sorry, I guess I misread/misunderstood your initial point.

Also agreed

Jatmobil

LOL! Sorry for going all nerdy on ya'll!!