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2.0 TFSI misfire at EXACTLY 3500rpm

6K views 5 replies 6 participants last post by  uwishuknewm3 
#1 · (Edited)
I've got a 2015 S3, which just developed a misfire at exactly 3500 rpm under load. Not 3400, not 3600, but 3500.

Some back story: For the past 3 years, my car has always suffered from random misfires while cold for the first 30 or so seconds. Dealership replaced plugs, coils, cats, dumped the tank, they couldn't figure it out. I decided to live with it, as I've read others had a similar issue, so fine.

Fast forward a few years: It begins this new misfire that is as dependable as the sun. There is no cel light, and the only code logged for the engine is a 'bus communication' code, which reports as happening only once in the past few weeks. I drove with my obdeleven logging all cylinder misfires during my 1hour / 30 mile drive to work this morning, which showed about 20 misfires per cylinder for the whole trip.

I can dependably cause this misfire at 3500, without fail, while under load at 2nd, 3rd, 4th and 5th gear.

I'm already on my 3rd set of plugs and coils. The first were replaced from Audi from suspicion, then I replaced them per-scheduled maintenance. I ordered a new set just this morning, again for maintenance, but I'm sure that's not the problem. Based on how reliable this misfire is, I'm leaning towards the computer. No mods at all, except for resonator delete from ECS, which I did over a year ago.

Thoughts?

btw, ~ 67,000 miles
 
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#3 ·
I think the activation of the tumble flaps (in the intake manifold) occurs at 3500RPM. Either there is a vacuum leak in the actuator (or its vacuum lines or solenoid valve), or the flap is sticking, and not moving properly. A vacuum leak can cause a lean mixture condition (causing a spark miss), or , if the flap is in the wrong position, a lean condition can also occur because the airflow into the cylinder is not correct, due to the incorrect position of the flap.
 
#6 ·
This is crazy i ran into this post because my car does the same thing. I have a 2014 GLI Gen 3 and mine cuts out about 3,600 RPM. It has done it ever since my turbo was replaced and i have always thought it was the tune put back on the car from the shop that did the turbo install. It feels like the boost cuts out when close to those RPM numbers and im guessing mine are different because my gears are very long. Hoping it is the boost cutting out but after reading this im going to start running some diagnostics. Ill keep you informed if it is related to this problem.
 
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