Rough / stuttery engine at 1100- 1400 rpms...

[Tigger]

Hey all!

I am posting in this section as I hope that you guys with a GTI (same / similar) running gear to mine may have some ideas...

My 2012 Octavia VRS has developed an issue that has perplexed me and several mechanics.
Your help or ideas would be greatly appreciated please!

At any temp below the magic halfway 90 degrees, the engine stutters and coughs at the rev range of 1100-1400 rpm...

I noticed it particularly in slow traffic such as going at 40kph through a school zone.

We have checked and swapped over coil packs.
We have replaced the PCV valve assembly.
We have performed a full DSG service.

No error codes appear....and the issue goes away when warm (90 degrees or more)

Help!

Any ideas?

Thanks

[Idle]

It's quite likely in the fuel system — going to idle supply too early, perhaps. I'm not all that clued in on current VW petrol systems, mine have both been diesels.

You do have a clean intake manifold etc, and no air leaks?

[Tigger]

I'll check those suggestions thanks "Idle"

[Reedy]

I had a very similar problem if not the same. Not sure what fixed it as I changed the high pressure fuel pump, cam follower and the MAF at the same time. Car runs loads better. I'd first start at the cheapest. Although my cam follower is the new role type it was fairly warn, try this first, then perhaps test the MAF or pick up one from the wreckers. Also my fuel consumption dropped down nearly half a litre per 100klm.

Good luck


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[Tigger]

Thanks Reedy!

[GTICam]

I had exactly the same issue with MY10 GTI.
After changing the PCV and swapping ignition coils to no avail, I removed the intake manifold and cleaned the (considerable) carbon deposits from the inlet valves.
Problem solved. Runs like new, so much smoother at low revs. On average over the last 5000km, since cleaning the inlet, the fuel economy is 0.6L/100km better for the same driving.
It's a big job to do though. You'll need injector seal kits and the tools to remove injectors from the head if they're stuck (I had 2) and also some tooling to fit the new HP injector seals and "calibrate" them. You'll also need a spline drive socket to release the lower inlet manifold brace from the engine block. That's about it for special tools. Have a look for "The Humble Mechanic" on Youtube. He's got a very good video of the removal and installation of the manifold.
Be careful with the electrical connectors too!
I think the problem comes about because of the position of the inlet flaps at low engine speeds and the flow divider plate in the head. The carbon deposit was causing restriction in this part particularly.
VAGCOM didn't show any faults and data logging showed the fluctuations at low revs as the engine management tried to compensate for the partial blockage in the inlet tract.
Hope this helps.
Cheers. Cam

[duck]

top end clean solved it for me. what GTicam said - i had it done by the mechanic it was around $500 for the job. My car had 128km on it by that stage, so it was well overdue for one.

Completely changed the way the car drove, from hump to champion.