I have a 12 year old Skoda Octavia mk3 TSI 1.4 with 155000 miles on the clock. It has JUST scraped through its MOT after repeated emissions failures due to carbon buildup. The mechanic has told me he doesn't want to see the car back next year as it won't pass again and cleaning the carbon deposit off wouldn't be worth it given the age and value of the car.

I've read a lot about Walnut Blasting to remove carbon buildup. Would it be worth it in my case or is the mechanic right, and I should just look to run it into the ground and get another car for next year?

Which measurement of the emissions test was it borderline on?

There may well be other factors unrelated to carbon build-up that could be responsible. I'm curious to know why this tester is sure that carbon accumulation is the problem.

5 hours ago, Breezy_Pete said:

Which measurement of the emissions test was it borderline on?

There may well be other factors unrelated to carbon build-up that could be responsible. I'm curious to know why this tester is sure that carbon accumulation is the problem.

It failed on fast idle and natural idle. 1.52% CO, 328 ppm HV, 0.95 Lambda. So not even close!

Looks more like a dodgy lambda sensor in the exhaust system if CO and HC figures are high.

I don't know much at all about 1.4 tsi engines, but I'd be pretty surprised if carbon build-up in the intake was causing that.

Do you have any fault scans?

To clarify a bit more: the catalytic converter was knackered and had to be replaced (I know, madness on a car with 155000 on the clock but cheaper than a replacement car right now!). When the new converter was fitted, it JUST got through after oil change, spark plugs and fuel treatment. I was then told it wouldn't get through another year due to the carbon build up even with the new catalytic converter. That's why I'm asking about Walnut Blasting as an option.

I can't see it being wise to spend a load more cash on a walnut shell blast on a hunch from a garage who appear to apply a 'just change everything we can think of' approach to diagnostics.

Does the coolant temperature gauge sit at 90 after a few minutes running?

Edited 13 hours ago13 hr by Breezy_Pete

8 hours ago, Breezy_Pete said:

I can't see it being wise to spend a load more cash on a walnut shell blast on a hunch from a garage who appear to apply a 'just change everything we can think of' approach to diagnostics.

Does the coolant temperature gauge sit at 90 after a few minutes running?

This doesn’t sound like carbon buildup to me. I don’t know that much about this side of engine maintenance, but surely if carbon buildup was to affect things enough to fail emissions, OP would be seeing a lot of other symptoms? I.E. issues with idling, fuel economy and performance?

Clogged air filter or dirty sensors on intake side??

does the engine consume any oil between services? as thinking what would cause a cat to fail

That's the thing, the car seems to have been running fine. Yes there's a bit of rattle but then again it's done over 150k. Fuel economy seems to be ok, and I haven't noticed a huge drop in responsiveness. What else could cause such a huge increase in emissions from last year?

worn piston rings? does it consume any oil?