s3 8l bam, missing at idle

J Eyo

Polo GTI (6) R
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Hi guys

So the list of mods:

- 3" custom downpipe/decat and 3" "catless" back exhaust system
- 42 draft designs intake
- 3" TIP
- n75H ECS racing valve
- Turbosmart Kompact DV its a full recirc valve
- PCV delete/ catch can install
- N249 delete
- 600x280x76 2.5 in/out FMIC sitting in pieces ready to go on

car has been fine(ish) up until about a week ago (about a week or 2 after I fitted the turbosmart Kompact plumb back DV, which flutters quite a lot - and n75H from ECS things have gone a little rough), always had the pressure drop between intake and dv code since buying it. But now at idle, instead of just fluctuating a bit, it feels like its skipping a beat quite consistently (fine under throttle, though the turbo seems to have become rather inconsistent but when consistent pulls really hard!) The idle misses badly enough for what sounds like knocking to occur, (checked oil levels just incase, all good here) the problem is pretty severe, it can make the whole car jolt and shudder and it almost feels as if the engine cuts out momentarily sometimes. Coilpacks are the recalled model, plugs are only about 3 months old.

MAP has been cleaned but didn't make much of a difference. There's no spacer in the post cat lambda (never had a cel though, but possibly lambda problems?) old worn or blocked injectors maybe? bad fuel filter, fuel pump? Id have thought these would have thrown codes?

no missfire codes either.

one thing, when i used to unplug the EGT the fluctuating idle issues vanished, I haven't tried this again yet as I want to get clear codes.

Unplugging the MAF makes no difference at all.

Cleared all the codes with vcds-lite before really taking note of them (id done things like unplug the maf, egt, disconnected the batteyr etc so had a ton of codes that wouldn't give me a clear reading), will take it for a spin today and rescan to see what I get

I do need to add, I changed the coolant temp sensor to reveal my thermostat is gone, car never gets above 70 when driving, most the time sits on 60 (climate control says about 55) when driving. If I idle it will eventually hit 90 but drop the second I move. So that's on its way, will change it on monday, could this be the cause? This has been the case for about a month though and these rough idle symptoms seem to be new.

Another note, once or twice its felt like this before when my fuel gets really really low, fuel pump on its way out maybe?

ideas?
 
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Have you checked the gaps on the spark plugs? I chased a misfire at idle once, turned out to be a dud plug gap. Your boost issue could be a weak waste gate? Are your breather pipes ok? Vac pipes under the manifold ok?
 
Try swapping your DV and N75 for the original-tried and tested to work-parts. Clear any fault codes, I can pretty much guarantee they're the cause of your problems.
 
Have tried all combinations of entirely stock with just one thing bolt on step by step and nada. I'll check my spark gaps maybe but it's onty a recent development epuldnt this have begun the moment I put the nkgs in?
 
If the stat is preventing the engine from warming up properly you will have a couple is fuelling related issues here... one will be that you are in permanent enrichment for cold start... the other will be that lambda control typically doesn't kick in until 70 to 80 degrees (would have to look at the maps to confirm)... the symptoms you describe suggest the misfire is due to the AFR being too rich...

I would suggest you fix the stat issue as you need the engine to be close to working within its designed parameters before you can possibly fault find anything...

<tuffty/>
 
Did the stat a little while back, much better there, but still the missing. Feeling like it's my
Plugs, how fast do the copper nkgs wear out?
 
Typically copper plugs need changing around 10k miles or so but if they are fine under WOT then I doubt they are the issue

1,8t's aren't the best at idle as std... they aren't that smooth out the box...

If its still a little hiccupy on idle then its more than likely an air leak... only way to tell if visual checks are failing is a smoke test... I see it all the time... most of the cars that fail a smoke test don't look like they should but if there is a leak big enough to effect idle the smoke test will find it

<tuffty/>
 

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