Advice Needed! S3 Running Rough On Startup

[Nick_db]

Hi All!

I could use a few pointers as to why my 2007 S3 is running rough.
When I start the car up from cold it almost sounds like it's running on three cylinders with a rhythmic vibration whilst it's on choke at 1100rpm. After 40-50 seconds the engine evens out and sounds a lot smoother - still whilst on the high idle.
I get no warnings up on the DIS and have recently changed my PCV and DV. The car has 77k on it and I'm at a loss as it only happens when the engine is dead cold, once run it behaves as normal.
Any help would be greatly appreciated.

Thanks!

 

[prt57]

First thing I would try is some new plugs. NGK bkr7eix from a proper dealer like AKS or Awesome GTi and not EBay.
Do you have a mate who could lend you some working coils? Swop then over and see if that makes a difference. If you are running an aftermarket induction kit you could pull one coil off at a time. If the roughness increases that cylinder is ok. The one that does not alter is the faulty area.
As this could also be an injector, removing the coil one at a time could also reveal which injector is faulty. Could be just a case they need cleaning out.

 

[Nick_db]

Ok, new plugs is a good start I will see if I can pick some up from AKS at the weekend... maybe a coil pack or two.
Sadly the car is 100% standard (so far ) so I can't quickly pull coil packs out but I might give it a try - the only limiting factor being that I need to let the engine cool again for it to start up and replicate the problem.

 

[Nick_db]

I didn't suspect the injectors purely because the problem only appears when initially starting the engine. Do the cleaners that you put into your fuel tank have any effect?
However I have noticed that the engine does seem sluggish to fire up too of late.

 

[paultownsend]

Look at my latest thread. OPIE oils currently doing NGK plugs and coils for less than £100 delivered. Got mine today. The coils look like quality items. It started raining so didn’t get chance to fit it all.

 

[prt57]

The injector cleaners will erode the plastic filter baskets so I’d say no.
If your at AKS at the weekend, ask them about it. They can do injector cleaning as well as everything else.

 

[samuelh_888]

The injector cleaner will move all the rubbish from the fuel lines into the injector, damaging the basket as Peter mentions above. This in-turn reduces injector performance/spray pattern.

 

[doce]

I have the same problem on a3 but only first ~5 - 10 sec from first cold start. Until now I replaced a lot of suspicious things and other valves except n75 valve and problem is still there. In my case, I know for sure it is not map, pcv, dv or spark plugs.

 

[Nick_db]

Last time I spoke to AKS they had a 2+ month lead time on booking in work!
I take it replacing injectors is a professional job too?

 

[torquemaster]

I had the same problems and in my case it was the fuel filter. If you didn t changed the fuel filter DO it!
If you never changed the coils do them also. No need to buy stamped vw ones, Bosh is the supplier and I recommend to stick with them. Don t put any other spark plugs then original cooper core Ngk.
Edit:
Just to clarify, the fuel filter has a pressure regulator built in.

 

[Nick_db]

Ok, so with 77k on the clock it's probably worth changing some of that stuff over anyway. Though I've never changed a fuel filter before so not sure how hard it is.

I did have one more idea also:

This cover on the top R/H side of the engine has leaked oil and maybe when the seal/gasket is cold it let's a little air in and ruins the vacuum inside the engine. Once the head warms slightly maybe the leak closes up?
Problem is that I'm having trouble identifying the part so that I can get a replacement.

 

[doce]

You can do a vacuum test. When you start the engine, try to open oil cap. If you can't take off the cap, then you have a vacuum problem. This problem with idle is very strange, I'm trying a few months to figure it out but unsuccessfuly. Fuel filter also replaced but the problem not fixed.

 

[ch1z64]

Firstly , if it was me I would get someone with a genuine cable to do an Autoscan and check car then from there I would try elimating problems , I am guessing you have had the car scan already

 

[Nick_db]

Yes, no apparent problems and this problem only occurs when the engine is dead cold!

 

[ch1z64]

Yes, no apparent problems and this problem only occurs when the engine is dead cold!

It's not a problem if it's not showing up on an Autoscan with a genuine cable .

 

[doce]

It's not a problem right now but it will become a problem very soon.

 

[Nick_db]

Ok it's update time!

New coil packs, plugs, PCV, DV and fuel filter fitted with the latest revisions and still no joy.
AKS very kindly agreed to squeeze me in and scan my car.
The mis-fire count on cylinder no. 3 was through the roof on idle but was running fine on throttle. They have diagnosed a clogged injector and will remove/test/clean them all for me along with a Walnut Blast to the inlet manifold (I think).
Hopefully this will be the end of my woes, the only problem is that I have a six week wait until I can get in with them. AKS seem to have very high standing on here and from talking to them I already trust them more than the local garage - whom I only use for servicing.