Lower RPM misfires S3 2007

[ILLUXN]

Hi there,

Long time lurker, first time poster. I've been enjoying my S3 MTM for a few months now. However, lately when coming home from a 20 minute drive (with some pulls, but nothing too heavy) and the last 5miles were driven at slow (city) speeds. I came home to something really odd, my S3 was misfiring all over the place, litterally as I pulled up the driveway, I was unable to properly drive the car anymore. I left it to rest till the next day and called my mechanic. He spend a good 4hours trying to figure out what was causing the misfires, but without succes. We hooked up the VCDS and as we suspected, misfires all over the place, on all 4 cylinders. Fast forward like 20minutes of idling the car with the VCDS hooked up, the car was running smoother and smoother. All of the sudden the misfires just stopped happening. I've been driving it ever since, and I have noticed some "smaller" misfires are still happening, at the lower RPM levels, but still very easely drivable. The car still pulls like a truck when you floor it, but what happens is when you have actually floored it, the next pull will feel slightly 'off' and I have less throttle response. My question to you guys is what could be causing this.

Apologies for the wall of text. I'm trying to be as clear as possible, and my excuses for any grammatical errors, I'm from Belgium.

I've got a video I recorded to show my mechanic, right when the first misfires were happening:



My S3 is a model that has been built by MTM from factory. It however currently runs slightly more horsepower than stock (it was 330HP stock from MTM), but I am running 380 with a new LPFP and HPFP (LOBA) + a custom remap.
I have brand new performance sparkplugs(NGK 8 or 9) and R8 coils.

We have tested so far:
-New sparkplugs & coils.
-Compression test: only the first cylinder was running a little less than all the other 3 (slap me in the face, but I can't remember the values).
-Battery is 6months old.

Cheers!

 

[nluk100]

Might just be a bad batch of fuel. Have you replaced your fuel filter recently?

 

[ILLUXN]

Might just be a bad batch of fuel. Have you replaced your fuel filter recently?

Thanks, last time we did an oil change we didn't have a new fuel filter lying around. Since it was changed only 3k ago, we figured to wait till the next oil change. I've ordered a new fuel filter yesterday. Sadly I have to wait till next week to test it since someone hit my S3 whilst parking his van, and it's sitting at Audi atm. Thanks for the input, that's the first thing I'll change!

 

[spawn616]

these cars are very fuel sensitive.. in my car just changing brands caused my car to ****** timing, so maybe change filter and runs sometime of octane booster just in cases

 

[ILLUXN]

these cars are very fuel sensitive.. in my car just changing brands caused my car to ****** timing, so maybe change filter and runs sometime of octane booster just in cases

I will deffo change the fuel filter, but I don't really want to change the fuel I use, since it's the best we can get here in Belgium. Octane boosters, are you sure about that? Also, my car was mapped using this fuel brand.

 

[nluk100]

What brand and octane of fuel are you using? 3k for a fuel filter is nothing so it's not that.

 

[spawn616]

in my country it is a must, if your car was mapped toit then should be fine but also where you filled up might have cleaned their tanks or theres water in there systems and and, also check if the filter was changed, if is an audi dealership more than likely it was stamped to be changed but not changed, sometimes you just get bad quality fuel

 

[ILLUXN]

I'm using TOTAL fuel station, if you guys have that over there? It's about the best you can get here in Belgium. I will deffo check the fuelfilter and change it as I ordered a new one already. I just have to wait till next week when my S3 is restored by Audi (bodywork). I'll keep you guys updated, as I'm a 100% commited to try and fix this, I'm going to try and get to the bottom of this.

 

[fernando young]

probably a vaccum leak? check out the PCV route, the PCV inlet on the plastic manifold.
maybe silly thing like the oil cap, or the MAF disconnected

do you have any other sound with the rattling?

 

[ILLUXN]

Small update:

- Changed the gasket on the engine (the upper one) since it was leaking a little bit of oil this weekend.
- Replaced the fuel filter(!)
- Installed a CTS catch can

First impressions: Wow, the car runs waaaay smoother after a few miles and getting the engine to warm up again. Did some minor pulls, and some slower engages (which was the most common time for the misfires to happen) and I didn't feel any more misfires. Today I did a small drive around town (+- 10miles) and everything was still fine, car was running really smooth. However as soon as I came home and parked the vehicle, right before I was about to shut down the engine the check engine light came on. The car however drives really well, and I'll be scanning for error codes tomorrow. Since I installed the CTS can, I checked for any vacuum leaks, but so far all the seals were okay.