A5 MT5 PD Rough Idling at lights

[Sloose]

I notice sometimes (regardless of ambient air temp, summer or winter) that when I idle at a stoplight, i get a rough idle at 800rpm...the whole car seems to shudder. If i blip the throttle, it goes away while the RPM is up, and shdders again at 800 rpm...


The act is random and hard to reproduce so i've been reluctant to bring this issue to my dealer.. It has been happening randomly since the car was new. Anyone experienced this?


Othewise the car runs like a top...37k on the Odo...

 

[DrewD]

Yes, this issue is very common but to varying degrees of severity. Mine does it but it is only an annoyance and others shook so bad that it would loosen their fillings.

 

[eluwak]

I've noticed this too... It's not bad for me but the first couple of times it was somewhat disturbing.

 

[Driver_found]

Me too. Comes and goes. In my case, seems to be related to fuel quality from different stations. A dose of Stadadyne or Powerservice seems to tame it.

-Mike

 

[Tim Birney]

Not that 50 or 100 RPMs would make that much difference, but my car does idle between 800 and 900 rpms.
Next time it happens, see if you can slowly increase the RPMs, and note where the car smooths out.

 

[Sloose]

Not that 50 or 100 RPMs would make that much difference, but my car does idle between 800 and 900 rpms.
Next time it happens, see if you can slowly increase the RPMs, and note where the car smooths out.

yeah that works (tried that many times...)


just someties the car shakes to hell at idle..I dont think its fuel related either - as it could happen at one light, and .25mi away not happen at the next light

 

[fireice]

search the forum.. has been discussed before...

mine does it too.. it is not rough idle (at least not mine).. more like pulsating sensation (engine slow-down)... happens only when engine is at operating temperature and you come to a stop usually after cruising...

the fix is to richen the fuel mix at idle- done via changing a value in one of the cells in the comp..ie.. reprogramming..

 

[Lightflyer1]

I have had this happen to me as well, usually after slow rpm cruise and coast down in gear to a red light. Doesn't happen any other time, and then only very occaisionally.

Would this reprogramming be done through VagCom or RocketChip type methods?

 

[GoFaster]

The "slow down shudder" that was fixable by VAG-COM adjustment of injection quantity on the distributor-pump cars, is a completely different issue from the rough idle on the Mk5 TDI.

 

[Tim Birney]

yeah that works (tried that many times...)


just someties the car shakes to hell at idle..I dont think its fuel related either - as it could happen at one light, and .25mi away not happen at the next light

I meant to imply that you would slowly increase the RPMs until smooth, and note what apparent RPM the smooth operation returned, I.E 850? or 900?

The car should idle between 850 and 875.
If you are idling at 800, then you are too low, and the dealership should be able to locate the fault.

How many miles on the car? Fuel Filter was last changed...when?

 

[Strider]

I meant to imply that you would slowly increase the RPMs until smooth, and note what apparent RPM the smooth operation returned, I.E 850? or 900?

The car should idle between 850 and 875.
If you are idling at 800, then you are too low, and the dealership should be able to locate the fault.

How many miles on the car? Fuel Filter was last changed...when?

Are you sure about that? My A5 will idle at 800RPM (as reported by VagCom) until the cows come home, unless I'm running heavy electrical loads. If I say, turn on the aux heater, the heated seats, and the rear window defroster, it will bump the idle to about 1000rpm. Once the load is reduced though, it goes back to 800.

Thankfully, though, once its warm it just purrs away quietly at 800.

 

[fireice]

forgot to mention- turn on ac and the pulsating goes away... i assume when the compressor engages the ecu raises a bit the idle rpms and thats enough to smooth out the engine...

 

[tdi06]

Mine does it too. Took the car back to the dealer and they kept it for two days trying to replicate the problem, but no luck. Car came back and still does it.

 

[53x19]

Here is the original thread - http://forums.tdiclub.com/showthread.php?t=145577&highlight=rough

I'm dying to hear if anyone has solved this. I'm still experiencing it, to my annoyance.

 

[Tim Birney]

Are you sure about that? My A5 will idle at 800RPM (as reported by VagCom) until the cows come home, unless I'm running heavy electrical loads. If I say, turn on the aux heater, the heated seats, and the rear window defroster, it will bump the idle to about 1000rpm. Once the load is reduced though, it goes back to 800.

Thankfully, though, once its warm it just purrs away quietly at 800.

My car (stone cold) will idle just a hair under 900 rpms, and when at full operating temp, somewhere in the middle, supposedly 850 rpms.
I've never experienced any rough idling. I'll have to connect my VAG and see what it reports.

 

[Imarobot]

I've been dealing with this since the first month that i've owned the car.

Sometimes it happens, sometimes it doesn't... I agree that it "seems" to happen most often after cruising for a while at low rpm and then coasting up to a light.

If I bump the RPM's it stops, but as soon as it drops back to idle it comes back.

I tried complaining to the dealer about it but of course they couldn't reproduce the problem.

I've just come to the conclusion that it is a "quirk" I have to live with for now... >.<

 

[10-cc]

I had the same problem @ 20K changed Fuel Filter and had no more rough idle (the one that goes away with the A/C on).

Two day ago the problem started again @ 23K.
And yes it usually comes up after a long highway drive or coasting.

Dealer could not do anything they cannot increase the idle...
Hop it helps.