Sudden Rough Idle

jesus_man

Veteran Member
Joined
Nov 9, 2005
Location
North Dakota
TDI
2005 Jetta (gone), 2002 Passat (gone), 2009 JSW (VW bought), 2010 JSW
Car has 172k, just filled up yesterday at a station (Top Tier) that I frequent. Did my normal 35 mile commute (Drop kids at school) this am and all was good. Then about 15 miles into my afternoon commute, I noticed a bad vibration as I rolled to the first stoplight. Thought it was tire or something, but it was still there at a stop and went away as soon as I accelerated. Did a couple of mild "Italian Tuneups" and it seemed to smooth out a little, but still rougher than normal.

I ran the codes via VCDS and got the common ones I've been fighting for a year or more:
P2BA6 NOx Emissions exceeded
P048C Sensor for Exhaust Flap, Implausible Signal

What procedures can I run to begin a diagnosis? I am a novice user of VCDS FYI.

Thanks!
 

jesus_man

Veteran Member
Joined
Nov 9, 2005
Location
North Dakota
TDI
2005 Jetta (gone), 2002 Passat (gone), 2009 JSW (VW bought), 2010 JSW
I'm thinking it was a stuck injector that worked itself out. I do have a bottle of Liqui-moly fuel system cleaner, but I don't know how to run it in full strength form (ie. not diluted with fuel). I assume there has to be a way via all the ins and outs of the fuel filter cap?? Or am I asking for more trouble dislodging something else??

I do run schaeffer's fuel treatment in every tank, so lubricity shouldn't be the issue.
 

ksing44

Veteran Member
Joined
Feb 13, 2010
Location
Southeast PA
TDI
2010 Golf TDI
My car can do all kinds of strange things during a regen, including the things you described. The car might shake, the idle is high, it sometimes smells, and it runs with jerky accelerations... Sometimes it also feels faster! I think it just gets a bit more responsive because of the amount fuel being dumped into the system with the higher idle. I have a gauge the shows EGT, so I can confirm it's just a regen when the nonsene begins and ends.

I have a 2010 Golf TDI with 190K miles and I owned it since new in April 2010.
 

jesus_man

Veteran Member
Joined
Nov 9, 2005
Location
North Dakota
TDI
2005 Jetta (gone), 2002 Passat (gone), 2009 JSW (VW bought), 2010 JSW
I know it did a regen recently, but I think it wasn't on that day. Aside from smell, cooling fans and high idle, I've never had anything funny happen during a regen, but I'll certainly watch for it.
 

jesus_man

Veteran Member
Joined
Nov 9, 2005
Location
North Dakota
TDI
2005 Jetta (gone), 2002 Passat (gone), 2009 JSW (VW bought), 2010 JSW
Making the assumption you don't know what a regen is, there is a system in modern diesels (2003+ IIRC) where they have a catalyst that burns off bad fumes coming from the combustion cycle. These fumes create a build-up on the catalyst and need to be burned off. Original systems used diesel fuel to burn off the build-up, whereas more modern ones use DEF. So when the car is injecting diesel into the catalyst, this is know as a regen. For most, we know it's happening because the rpm's are elevated to around 1,000 and the cooling fans turn on.
 
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