Q5 TDI Rough idle when cold
01-01-2014, 05:28 PM
#21
Audiworld Junior Member
Thread Starter
Join Date: Dec 2013
Posts: 17
Likes: 0
Received 0 Likes
on
0 Posts
By "when cold" do you mean the engine, or the air temps? Does the TDI engine in your Jetta record misfires? I wonder if, since this seems common between your car and others, it's just "one of those things" that they all do? It could be that one cylinder just doesn't warm up as fast as the others? I know my diesel tractor will run really roughly for the first few moments when it's cold, even if I glow it well.. I can tell it's running fine though, no black smoke. With the modern engines, that's a little tougher, since there's so much keeping the smoke from coming out. =)
Not sure if it is recording any misfires or not. I should take advantage of our cool weather and collect some data.
Today for instance, we went up to my favorite volcano for some fresh air and sunshine. A ~2 hour drive up, then sitting for ~3 hrs in upper 30's to low 40's produced a smooth re-start. There was still heat in the cylinders from the drive up so, no issues.
I was reading about the cooling system on the Q5 TDI and noted how they placed special emphasis on heating up the engine as soon as possible. Since this engine is for mainly used in upscale vehicles, it would make sense that more effort was expended in the NVH area than what was spent on the 2.0 TDI installed in the Jetta. Funny thing is that my ALH '01 did not have this issue.
Thanks for the reply
01-01-2014, 07:05 PM
#22
Audiworld Junior Member
Thread Starter
Join Date: Dec 2013
Posts: 17
Likes: 0
Received 0 Likes
on
0 Posts
in my case it was not a Q5, but a 2013 Q7 TDI dealer loaner. I perceived some idle vibration, more so when cold. Another order of magnitude different than my W12, meaningfully more than my 4.2 V8 gas, and more than a gas V6 Audi I owned in the past. More than the gas portion of my current four cylinder 2.0T Q5 when running on the gas side. On the other hand, I've been in a Cayenne TDI several times in recent days (as a passenger), and in that application and seating position it seems pretty darn smooth at idle; not meaningfully different than other V6 gas experience in similar conditions.
That Q7 TDI had 2500 miles on it, almost new looking inside and out, and no obvious issues. Q7's are now way long in the design tooth, and maybe the motor mounts or something were another step behind generation wise.It is also at a marginally lower tune than the Q5 TDI, and the Q7 is a real porker weight wise. Still my question there was about the NVH (and possible boost lag), not the heft or acceleration, which was decent. Some incremental idle vibration doesn't surprise me in general given both the higher compression and the self ignition. Much less than older diesels. But it was perceptible in both the steering wheel and even in the pedal some if I was thinking about it. Not like a rude heavy duty/construction type vehicle by any stretch, but also not transparent.
I was interested in it for a possible alternative to a 3.0T, but unfortunately ran into some pretty over the top zealot stuff on the other board where I had the vehicle interest and couldn't get a direct answer to what I had run into w/ the Q7. It was kind of a turn off.
That Q7 TDI had 2500 miles on it, almost new looking inside and out, and no obvious issues. Q7's are now way long in the design tooth, and maybe the motor mounts or something were another step behind generation wise.It is also at a marginally lower tune than the Q5 TDI, and the Q7 is a real porker weight wise. Still my question there was about the NVH (and possible boost lag), not the heft or acceleration, which was decent. Some incremental idle vibration doesn't surprise me in general given both the higher compression and the self ignition. Much less than older diesels. But it was perceptible in both the steering wheel and even in the pedal some if I was thinking about it. Not like a rude heavy duty/construction type vehicle by any stretch, but also not transparent.
I was interested in it for a possible alternative to a 3.0T, but unfortunately ran into some pretty over the top zealot stuff on the other board where I had the vehicle interest and couldn't get a direct answer to what I had run into w/ the Q7. It was kind of a turn off.
Most NVH issues were taken care of at the source by the pilot injections that common rail allows. The single large spray that mechanical systems provide is the primary cause of "diesel clatter". Our common rail systems pilot injections start the fuel burn with smaller amounts thus reducing the clatter.
01-03-2014, 03:57 AM
#23
AudiWorld Senior Member
Mine sits in a heated garage but I have seen -20 on the dash at least once this winter. After sitting outside at work at zero it took a couple seconds to start but no issues. I do use some anti-gel as I did with my F-250 diesel... have to admit when it is really cold I do worry a little but nothing so far- knock on wood.
01-03-2014, 06:14 AM
#24
AudiWorld Member
Join Date: Jun 2013
Posts: 152
Likes: 0
Received 0 Likes
on
0 Posts
no problems yet... but the real test comes this week
I have had no problems starting, or rough idle. My car is parked overnight in an unheated but insulated garage, and it rarely gets below 32F sitting there.
However, it does sit outside for roughly 11? hours/day at work. The real test will come in the next few days with bone-chilling temps here in the metro NYC area (I know, it's nothing compared to you hardy souls up in Canada). I'll report back if I see any rough idling.
But so far, no problems with my TDI. Cheers.
However, it does sit outside for roughly 11? hours/day at work. The real test will come in the next few days with bone-chilling temps here in the metro NYC area (I know, it's nothing compared to you hardy souls up in Canada). I'll report back if I see any rough idling.
But so far, no problems with my TDI. Cheers.
01-17-2014, 07:40 PM
#25
Banned
Join Date: Mar 2010
Posts: 433
Likes: 0
Received 0 Likes
on
0 Posts
Yeah. It happens after threads get hijacked and steered off-topic to a different model like the Q7. What else can you expect? Keep it relevant to the A8 and Q5 or post it in the Q7 section where it belongs.
Thread
Thread Starter
Forum
Replies
Last Post
Alexandroff
A8 / S8 (D3 Platform) Discussion
2
11-21-2017 01:45 PM
vwleadfoot
Audi Original "S" Cars
4
12-24-2015 06:07 AM
