Sudden Rough Idle

[jesus_man]

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]

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]

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]

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.

 

[Sparkles]

Can you share what you mean by "during a regen"?

 

[jesus_man]

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.