o2 sensor failure?


New Member
Hey guys, over the past few months a bit of an issue has developed with my 05 AUDM type s. The car has a tegiwa intake, toda racing header, nvidia n1 catback, no cat, stock internals and a ktuner ECU. The car came with all of these mods installed. The first sign of any problem was a very low idle briefly on cold starts (450-550rpm) which would sputter for a few seconds and then restore itself to normal idle range, this would happen occaisionally and began to occur progressively more often, but always sorted itself out within a few seconds and a couple blips of the throttle. Throughout this time i would occaisionally have a p0420 code pop up, usually while just cruising on the freeway, which i was told was due to the cat delete. I cleared this code with a Lufi digital gauge that came with the car, this code appearing had no direct correlation to any of these idle problems, and the car in its current state doesnt actually throw any codes. Recently however one morning it began sputtering and smoking (rich) and drove terribly - throttle response was awful, rpm would drop much faster than usual when depressing the clutch and would almost stall, jerky acceleration, sounds quite rattly aswell compared to how it should normally sound. Before these major problems surfaced, i also had one sole instance of the engine inexplicably turning off while idling, the engine has 225,000km on it or 140k miles. Could these issues be attributed to a primary o2 sensor failure or am i looking at something a little bit worse? Cheers. (Update) I’ve pulled the spark plugs which are all black as, and have had a peek down into the cylinders, 1 to 3 are all evenly black/sooted, however cylinder 4 has a roughly 2 square centimetre, irregularly shaped clean spot in the centre, no signs of damage to the cylinder surface or the spark plug itself. Hmmm.

For anyone else who may encounter these problems, it turned out to simply be the coil pack haha, replaced packs and plugs and she’s running beautifully again.
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Advanced Member
Hi there.

When the primary O2 went on my DC 5 there were no major problems. However the lack of performance was noticable. After it was replaced the EML went out and the car returned to normal.

I recently had some over reving and idle problems on start up. My mate cleaned the IACV and that put that right.

I dont want to be the bringer of doom but your situation sounds a bit more serious. There again the engines are so tuned that a replacement O2 may put things back to normal. I hope so anyway and hope you get it sorted.

Sorry I have'nt got a definate answer but someone on here will hopefully be able to help.