VRS issues at 3000rpm

[jamesmall]

I have a MK1 Octavia VRS

 

Lovely boost in lower gears, runs nicely when driving easy

 

The problem arises when under hard acceleration, usually 4th or 5th gear and upwards of 3000rpm

 

I can feel a misfire whilst accelerating, and after that it goes very lumpy in all gears.

 

The car will accelerate- just- but very stuttery and lumpy, regardless of what gear im in after the initial hard acceleration. Sometimes you can accelerate through it, other times not.

 

Recently I have replaced all spark plugs, coolant sensor and thermostat. Also performed TB clean and alignment, and full service with filter changes etc.

 

Any suggestions? The fact that it boosts fine in lower gears and runs nicely while going slow would seem to eliminate air flow issues wouldn't it?

[jamesmall]

Meant to mention, did a VCDS scan, came back with

 

17704 and 17705 which are frequent as far as im aware. No other faults logged

[jamesmall]

Some further research has suggested possible coil pack issues?

[kentphil1]

Check your breather pipes - especially the Y pipe and the S pipe under the manifold down to the PCV valve. Unmetered air is getting in somewhere.

 

Edit - just seen your coil pack post - check with your local Skoda main agent as there is a recall on these items, you could get 4 nice shiney new ones if your car has not been done yet.

[YellowCar]

Must admit whenever I hear those symptoms my first thought is coil packs. Probably won't log a code until they're about to melt. But also with the code you've got that's a +1 for checking pipework.

You could also try a short run with MAF unplugged see if it runs smoother, if so it's maf sensor, don't worry if your traction control light comes on after doing so. Can clear it easily.

[Mankee]

17704 could be the temperature sensor. Have a read of this:

 

http://wiki.ross-tech.com/wiki/index.php/17704/P1296/004758

 

17705 can sometimes be caused by a remap. It's a bug in the original software that manifests as this fault code when the mapping is altered. It can be patched by the likes of R-tech, Shark etc.

 

Sorry, I'm an idiot and missed the bit where you said you'd already changed the coolant temperature sensor. Doh!

[jamesmall]

Check your breather pipes - especially the Y pipe and the S pipe under the manifold down to the PCV valve. Unmetered air is getting in somewhere.

If this was the issue, wouldn't it be apparent in all gears and rpms?

 

Must admit whenever I hear those symptoms my first thought is coil packs. Probably won't log a code until they're about to melt. But also with the code you've got that's a +1 for checking pipework.

You could also try a short run with MAF unplugged see if it runs smoother, if so it's maf sensor, don't worry if your traction control light comes on after doing so. Can clear it easily.

Well a coil pack isn't a disaster. As above, wouldn't a MAF issue cause problems at any rpm?

[YellowCar]

Can do, but getting through 3000 rpm is getting up to high levels of intake so will highlight an issue. It's one of those things that costs nothing to check though isn't it.

Was it a gen temp sensor by the way in reference to Mankee's suggestion.

P.s unpicking my melted coil pack from the chamber was a bit of a disaster as it goes, check with your dealer for recall as Phil suggested.

Issues with split pipes can be a bit random, depends what is split and how really.

[jamesmall]

It was a genuine VW one yeah

Would I be OK to unplug the MAF and rev it right through the range? Bit worried about making it worse

[kentphil1]

Unplugging the MAF will simply mean that the ECU will default to inbuilt fuel trims to run on instead of real time ones from the MAF. You should be ok in that respect.

[kentphil1]

If this was the issue, wouldn't it be apparent in all gears and rpms?

 

Well a coil pack isn't a disaster. As above, wouldn't a MAF issue cause problems at any rpm?

Because the load applied by being in a higher gear places the induction system under greater scrutiny due the need to supply boost for a greater amount of torque to turn the gear, meaning that the fuelling needs to be more accurate.

 

Also the PCV valve is in circuit to the breather piping and so it opens and closes with crankcase pressure which means the system altering the fuelling as well if that valve is gummed up as many are.

[jamesmall]

Because the load applied by being in a higher gear places the induction system under greater scrutiny due the need to supply boost for a greater amount of torque to turn the gear, meaning that the fuelling needs to be more accurate.

That makes an awful lot of sense, and to my non mechanic mind, seems to explain the problem that exists. I'll unplug it tomorrow and give it some welly in 4th and 5th and maybe this will indicate the issue!

[kentphil1]

I would make very certain that it is not coil packs though before you do that, as if you do have a fault with them, you will fill the cat with unburnt fuel - which will eventually render it fubar.

[jamesmall]

You could also try a short run with MAF unplugged

 

Unplugging the MAF.

 

Yellowcar and Kentphil- I want to have both of your babies

Unplugged this morning for a 12 mile trip to work- gave it my right foot and whooossssshhhhhhh she runs like a beaut :clap:  :clap:

Amazing how such a simple device can cause so much agro!

[YellowCar]

Did your tcs light come back on when you plugged back in?  If so, you can disconnect battery, will clear it, but then you may have a code pop up for a weak signal to something like airbag after disconnecting, don't worry about that either, just clear it next time you're on vcds, if it comes back, then worry.

 

Glad it appears to have been found, further suggestion, buy a genuine/bosch MAF - I'm currently running a spare pattern part one and its fine, ran one on a Seat and was fine but it is a bit of a gamble.  Been meaning to replace with gen but other stuff happens. 

 

Also, still ring your dealer, check for coil pack recall.

 

Once codes have been cleared after fitting new MAF, drive for a while, scan again just to make sure they don't popped up again, if so you'll have something else to explore.  But yes, the MAF can do some strange things when the sensor starts playing up.

[jamesmall]

it did put the TCS light on, again happy that you mentioned this could happen. No EML though. I have VCDS so ill run a scan and make sure its all tickedy-boo, but so far so good.

 

And yep Ill definately see if I can get the coils done, may as well if its on skoda!

[YellowCar]

I think euro car parts had a decent price on Bosch MAF recently as well...

[Gonzaga]

Log MB 015&016, misfire counter, via vagcom.

Value should be in all blocks 0 or 1, if its start to rise usually coil pack/packs are on its way out. 

Testing should be done in 3rd or higher gear, from 2000rpm and up.

Edited 14 May, 2015 by Gonzaga