Ok so my vRS tracktoy has decided to play up tonight, even though I spent several hours on it this week getting it ready to be remapped by R-tech.

Basicly for the last month or so, I have been running it at 1.4bar (20 - 21psi) with no issue's at all.

The car has pro alloy front mount, 3" downpipe, piper catback, forge dv, new coilpacks and new spark plugs, sai removed and n249 bypassed.

As said it's been running fine for over a month with the map that is on it.

Yesterday I got around to fitting my forge TIP and ebay CAI kit (with a k&n filter).

As I took my time fitting the TIP & CAI and then spent the rest of the day / evening helping my mate put his LC back together I didn't get a chance to drive the car under load last night.

So tonight I took it for a blast.

All seemed fine, the car idles and drives as it should.

But when giving it some beans, it pulls hard upto 1.4bar as normal, but then the boost drops back to 1bar, then it starts fluctuating between 1bar and 1.45bar, until it hits approx 5500rpm and at that point it drops all boost (gauge reads 0) and then it will instantly misfire (assuming it suddenly runs mega rich).

It does this in 3rd and 4th, but I also managed to get it to do it in 2nd.

No engine managment light at all and drives fine off boost.

Has anyone come across this issue before ?

I am 99.9% sure all pipes are connected to the TIP propperly and nothing is loose or leaking.

Sounds a little like when my maf went. Try unplugging it for quick test.

Sounds a little like when my maf went. Try unplugging it for quick test.

Thanks I will give that a try.

Still seems odd that it was all ok before fitting the TIP and CAI though, but then I guess the maf's are not great on the 1.8t's anyway.

Yeah you could have broke it quite easily whilst fiddling with it.

I have read I think on vwvortex that some CAI causes the air not flowing properly and MAF detects some funky air readings. Put back the stock air filter housing and see if it happens again. Did you log misfire counter via vag com?

I have read I think on vwvortex that some CAI causes the air not flowing properly and MAF detects some funky air readings. Put back the stock air filter housing and see if it happens again. Did you log misfire counter via vag com?

No I haven't logged anything, I have also read that about the CAI causing air flow disturbance, but tbh I can't see it (sounds more like faulty maf to me).

Ok so I went for a drive earlier and it was doing pretty much the same thing, boost fluctuating and at 5500rpm it would drop all boost and misfire, also noticed the traction control light flashing.

So I pulled over and disconnected the maf.

Went for another drive, and the boost was all over the place, this time though it would keep fluctuating until around 6000rpm and then it would drop to about 0.5bar but rev up to about 7000rpm (didn't want to push it more than that).

So I swapped the maf with the 1 from my other vrs and cleared the fault codes that came up due to disconnected maf.

Went for another drive, the boost was still the same fluctuating, but again it would rev through it and at around 6000rpm it would drop to 0.5bar again.

So I am not sure now if I have a faulty maf or not, anyone have any more idea's ?

I've not tried refitting the standard airbox yet, as it's not a 2 minute job due to do.

Ok so now i'm even more confused.

I put the "suspect" maf onto my other vrs, and took it for a drive.

Once the car warmed up I put my foot down, I had 2 little surges of boost and then nothing, the car wouldn't boost at all (0.25bar) no engine management light on and no flashing traction control / ASR light, this car has an AVCR fitted, so the N75 has been mapped out.

Anyway long storey short I drove home, and put the original maf back on this car, and took it out for another quick drive, but still no boost.

I checked the fault codes and it had logged that the pressure had exceeded limits (sorry didn't make a note of the actual code / wording) but once cleared the car is running fine again (thankfully).

So back to the car that had the original fault, I refitted the "suspect" maf and checked for fault codes, once again nothing logged.

I went for a drive, and when giving it some in 2nd all was fine, in 3rd however it was doing the boost fluctuation still, but did rev to 6000rpm before dropping the boost back to 0.4 / 0.5bar again but no misfire for the first 2 or 3 runs, but then it started to cough and splutter again around 5500rpm.

Fuel pump starting to fail !!

Fuel pump starting to fail !!

I had wondered if it could be a fuel pump issue, but then putting the maf from this car onto the other and getting a fault thrown up as soon as I went on boost, put me off that trail of thought.

Fuel pump starting to fail !!

I had similar problems,example: 3rd gear 2000 rpm, pedal to the metal and boost starts to build up fine until approximately 3000 rpm then shi* start to happen. Peaks around 1.5bar then falls on it face to 1bar then up again and so on.

Due to lack of fuel in high revs ECU was pulling boost down to protect the engine, new pump has solved that problem.

I would also check MAP sensor because a year later a had similar problem but this time boost was jumping even harder and it dropped sometimes to 0-0.3 bar. New MAP sensor resolved that problem.

If your ASR/ESP light is lighted it`s probably MAF problem.

Edited 18 February, 201313 yr by Gonzaga

I will swap the fuel pumps over tomorrow, and if the issue moves from 1 car to the other, I know what to replace then

I had wondered if it could be a fuel pump issue, but then putting the maf from this car onto the other and getting a fault thrown up as soon as I went on boost, put me off that trail of thought.

Did you reset the ECU after the exchange?

Did you reset the ECU after the exchange?

No, there were no fault codes stored.

Ok it's not the fuel pump either.

I swapped the pumps over (complete with the sender units) and both cars run exactly the same as they did before (for info both cars run the same amount of boost, and have similar mods).

It seems if I am following some slow moving traffic for a few miles, then the misfire is worse (had it happen at 5000rpm in 3rd today and also on part throttle around 0.5bar boost when crusing).

So I have also spent the last 3 hours checking all vac hoses in the engine bay and all connections to the TIP just incase there was a split somewhere, in the end I got fedup and removed the N249, N112, did the vac line simplificaion and the evap simplification mods, as the SAI was already removed it wasn't too bad a job to do.

Anyway the only leak I can find, is in the plastic hose that connects to the brake servo, and it feels like a pin hole where it connects to one of the 1 way valves (the one by the maf). So tomorrow I will sort that minor leak out, but other than that, I guess it will be a case of refitting the standard airbox to see if that fixes it.

I checked in vagcom and there is no misfires being recorded / logged either.

Fuel filter been replaced recently ??

Fuel filter been replaced recently ??

2011 iirc, but i'll pick 1 up tomorrow if fitting the airbox back on doesn't cure it.

Don`t remove CAI just disconnect it at MAF sensor (leave the MAF connected), use some clean cloth (sock) and put it over the inlet of TIP to prevent debris get sucked into the turbo.

Edited 20 February, 201313 yr by Gonzaga

Ok I removed the CAI and refitted the airbox.

This made it slightly better, but the problem is still there (it doesn't fluctuate the boost quite as much, but it still has the misfire / splutter around 5500rpm).

I also changed the plugs again today, but that made no difference.

I have picked up a new fuel filter, but didn't get a chance to fit it today, so will do that tomorrow.

When I demonstrated the problem to a mate, he said it sounds more like a car using launch control than a misfire (which would make sense, as no misfires are being logged).

So I tried reving the car when stationary, and it does indeed start to crackle / miss, at around 5000 / 5500rpm (I didn't want to just slam my foot to the floor and end up bouncing it off the rev limiter in a car park,).

Do you scan with vag com for errors or do you log meas block 015&016 Misfire recognition in real time and watch the counter? Usually you won`t see misfire error stored in the log, the best way is to log it and gun it in 3rd gear.

Do you scan with vag com for errors or do you log meas block 015&016 Misfire recognition in real time and watch the counter? Usually you won`t see misfire error stored in the log, the best way is to log it and gun it in 3rd gear.

I have been checking for stored fault codes, but I didn't realise that I had to log the measuring blocks to know if the misfire counter had been activated, I assumed (wrongly) that if it had detected a misfire, it would update the misfire counter and also the counter per cylinder.

015 block is for cylinder no.1-3 and 016 block is for no.4 cylinder. You will see if the engine starts to sputter increase in value below in the box. This allows you to monitor every cylinder.

If the fuel pressure is at idle app. 2.5bar and at full boost 3bar+your boost level then probably one of the coils are failing.I can only guess ... I hope you will get to bottom of this, I`m really interested whats the problem.

Good luck!

015 block is for cylinder no.1-3 and 016 block is for no.4 cylinder. You will see if the engine starts to sputter increase in value below in the box. This allows you to monitor every cylinder.

If the fuel pressure is at idle app. 2.5bar and at full boost 3bar+your boost level then probably one of the coils are failing.I can only guess ... I hope you will get to bottom of this, I`m really interested whats the problem.

Good luck!

Thanks for the info

The coilpacks were new last november (skoda recall), so upto now i've been assuming they are ok, but I might swap them with the coils on the other car tomorrow (again new from skoda but only got these a week ago).

The misfire counter only shows full misfires. It may not show partial misfire. It can say all is well when it ain't.

It can say all is well when it ain't.

I'll put £50 on that being the case lol