So, my 2015 S3's CEL came on last week. It had just indicated it was due for its scheduled maintenance anyway, so I immediately scheduled an appointment for service. Took it in today and they said the computer showed a misfire at startup trigger the CEL. They pulled the plugs and inspected them and noted that allow four were "eroded". Replaced them with new plugs and cleared the code. Seems a little concerning to me because 20,000 miles doesn't seem like normal wear for plugs.

I'm a bit of a noob when it comes to things like this, so just wondering if someone could offer an explanation for why this would happen.

Always used 93 octance gas.

Thanks,
Shan3

 

Where are you buying gas? Chevron, Shell, 76?

 

I thought that too, but all 4 being bad at the same time?

I'm guessing the error will return - make sure you're using 91/93 Octane, because some stations flop the order at the pump. Also, does someone else drive the car that isn't paying attention to the Octane?

 

FWIW, I just spent over a month, going between two different garages, to troubleshoot an intermittent misfire condition on my '13 Jetta GLI. While it turned out to be a bad O2 sensor, which I suspected early on, I wound up traveling down a rabbit hole because the "non-VW/Audi garage" informed me that I had a lot of carbon build up, which was causing the misfire...subsequent research educated me that "this is a thing" with DI engines. I had taken it to them initially because I figured they could handle my 40k service, and they were just down the street from me. Car was running fine before then, and only started misfiring a few days after getting it back from them. I thought they did something like knocking a vacuum line loose to cause the misfire sometime during the service. Walnut shell blast, new coil packs, and new injectors did not solve the misfire.

Before getting the issue finally resolved, which had grown progressively worse, but still intermittent after a month, I checked the new plugs which were installed at the initial service, and they had a fair amount of carbon built up after only ~200 mi, from the car running rich over the past few weeks. But if your plugs are "eroded", you may have some fluid getting in the chamber somewhere. I had a similar issue when I had a crack in a cooling jacket in the cylinder head of my tuned Corrado. I don't remember the state of the plugs, or if they had enough time to corrode, from the time the car started running poorly, until I had the motor replaced. If you plan on keeping the car, try keeping an eye on the plugs, to make sure a larger problem hasn't surfaced.

Good Luck.

 

I'm the only person who drives it, so no chance of anyone putting regular gas in it. Always 93 octane. I use a few different local gas stations, but nothing that would be considered sub-par fuel.

A little worrisome that there may be a deeper problem. I've been holding off on doing a Stage I or II tune because I'm afraid that I will end up screwed on any warranty issue. This situation doesn't help make me feel any better about it.

Thanks to those who have replied.

Shan3

 

Shan, did they say "corroded" or 'fouled' (as in carbon fouled)?

 

The service ticket said "eroded". So, unclear what's meant by that.

 

Hmmm... oxidation and erosion, if true, is old-school issue with lead in the gas or moisture in the cylinder, I doubt either of these are the issue.

If it happens to a new set of plugs, yes there is real reason for concern - definitely hold-off on any mods on the engine or ECU till you can see how a new set of plugs wear.