Two Week Saga Continues - MAF or DV?

[NCRAW]

Hi all,

Two weeks ago as I left to head for a 3 hour trip only for my car to idle hunt at the first traffic light and the same on first gear when my foot off the accelerator. It also was taking its time to drop the rpms when my foot on the clutch and it was back firing when changing gears. I tried not to use the car while there and only tested it for the next couple of days where the problem seemed intermittent. Drove it back and had a BSH PCV fix waiting for me in the mailbox. Replaced the PCV and went for a spin and all felt ok.
I also ran a fault check via vcds and found that all cylinders misfired during the 3 days I was away (different times). I cleared the faults and went for a spin and all was clear when i did another fault test check.

However its never that easy. The car feels it's lacking boost and it comes on late. While it idles ok, its not perfect. I can still feel slight vibration in idle and sometimes it drops rpms (by about 100) and also sometimes hold revs before dropping while changing gears. Also sometimes the engine sounds a bit harsh and yesterday I heard a fairly loud backfiring from the exhaust when revved it to 5K at home (car stationary). I suspected the DV so pulled it out yesterday and had a look. Its a Rev G and it looked in really good condition, no diaphragm tear and felt ok when pressed on the seat.

Which leaves me with the MAF, that I will be testing tonight by unplugging it and going for a run. If it is the MAF, then is it possible for it to foul or fail at the same time as the PCV or is there some sort of r'ship between the two? should I try to clean it and how would I go about doing that?

Maybe there is a air/vac leak somehwere?

I'm running Forge Twintake, Miltek TBE resonated, APR Stage 2.

Any help or thoughts would be very much appreciated

 

[warren_S5]

Could be an air leak, but then it can be really hard to diagnose as I had an unexpected leak and tracked it down to a pipe that entered the engine block under the CAI hose beside the battery (I'll try and find a photo of it later ).

What age / mileage is the car? Some cars have had faulty valve springs, others coil packs, others dodgy spark plugs, so it is never easy to start diagnosing without spending a thick wodge of cash.

Only other thing it may be worth doing is running a shot of fuel injector cleaner through the fuel system. Are you running high octane fuel out there.

If you want to do some data logging to measure blocks head off to APR's site where it explains a number of methods for doing the various checks / data logging.

 

[NCRAW]

Hi mate thanks for info. It's a 2008 with 42,000 kms and been running perfect on stage 2 till the pcv crapped itself so I'm not sure if it's something serious or just a loose hose or bad maf. It's booked on we'd at the place I had all my mods done but I'm hoping to narrow it down. Yes if u have an image then that would be great. The other thing I can hear is a wooosh sound when pressing the clutch. It's not when taking foot of the accelerator. It sounds like it's coming from the dv hose running back to the air intake which might mean a faulty dv. I just can't see two problems at the same time.

 

[NCRAW]

Just an update. While searching for well priced dv in Australia (which is impossible as we get torn a new hole everytime we need a part) I found a new independent VW/Audi shop who were kind enough to check fuel quality and run a diagnostic and found cylinder 2 misfiring 6 times in about five min and cylinder three once which he think it's due to the coil packs as suspect one, then spark plugs and finally compression loss which he thought unlikely. I'm not sure how the pcv failed at the same time as a coil pack (if it's indeed the coil pack). Could a coil pack issue ie misfire cause a pcv fail?

Il call audi on Monday as there was a recall in aus on the packs so let's see.

Also what are your thoughts on getting new spark plugs after 42k on the clock. And if it's recommended then which brand and type?

Thanks

 

[warren_S5]

Just an update. While searching for well priced dv in Australia (which is impossible as we get torn a new hole everytime we need a part) I found a new independent VW/Audi shop who were kind enough to check fuel quality and run a diagnostic and found cylinder 2 misfiring 6 times in about five min and cylinder three once which he think it's due to the coil packs as suspect one, then spark plugs and finally compression loss which he thought unlikely. I'm not sure how the pcv failed at the same time as a coil pack (if it's indeed the coil pack). Could a coil pack issue ie misfire cause a pcv fail?

Il call audi on Monday as there was a recall in aus on the packs so let's see.

Also what are your thoughts on getting new spark plugs after 42k on the clock. And if it's recommended then which brand and type?

Thanks

PCV won't fail due to coil packs.

It may be worth swapping the coil packs about and seeing if the same cylivnders report misfires, or whether the misfires follow the coils. If they don't take the plugs out and check them and give them a very gentle clean with toothbrush and some electrical contact cleaner and reinsert.

I think you've done well to get 42k out of plugs, most don't get anywhere near that, there have been a lot of issues with plugs, see here: LINK

 

[NCRAW]

Thanks so much for the info. I'm all lost with the so many choices of plugs. I'm happy to try a full new set. I switched to stage 2 APR from stage 1 about 3000kms ago and have taken the car on a couple of mountain drives and wondering if it's just coincidence that pcv failed at the sane time asthe issue I have now. I'm willing to try a full spark plug set but which one should I go? The one recommended for stage 2+ since I'm going that path anyway?

 

[NCRAW]

Also what about the gap? Do I leave it stock. Honestly I don't want to mess with something like that.

 

[warren_S5]

Tough call, some are getting good results with the PFR7S8EG.

I suppose you could try the BKR7EIX or 8EIX plugs, but I'd only go with these if you do track days or really hammer the car about.

I think its worth getting a feeler gauge and ensuring all plugs are gapped to 0.8mm as this is the optimal gap for OEM. Your tuning house may be able to advise if you should adjust from this, but its a dark art so hard to recommend.

 

[NCRAW]

So the PFR7S8EG actually comes with standard 0.8 gap? The others I believe come with 1.1.

This car is my daily driver and I drive it not gentle nor I hammer it on daily basis. But I like to take it to the mountains a few times a yr for some hard driving. Maybe the 7EIX is a good balance though the S8EG would be newer and better than what I have in mine.