Hi all,

How typical is this.

My 1.6 diesel Octavia is always as good as gold until we go on holiday.

First start of the day, and it runs rough, 3 cylinders maybe.

After a couple of minutes it runs fine and is ok until the next morning cold start.

Any suggestions would be appreciated.

Not typical. Could be a failed glow plug.

I'm going with failed or failing injector. A glow plug would trigger the EML.

Thank you for your replies.

I have used a code reader which has failed to show any faults codes.

I have tested glow plugs 1,2 and 4 with a battery and bulb, they show continuity.

I am going to let my local garage have the car overnight, so that they can see it with a cold engine.

They are suspecting a failing injector.

47 minutes ago, johnkitchen said:

Thank you for your replies.

I have used a code reader which has failed to show any faults codes.

I have tested glow plugs 1,2 and 4 with a battery and bulb, they show continuity.

I am going to let my local garage have the car overnight, so that they can see it with a cold engine.

They are suspecting a failing injector.

Is it not possible to test #3 glow plug because of the sensor?

Number 3 does have a pressure sensor.

As I don't know how it works I thought best to leave it to the experts.

It started rough again this morning but sorted itself out after a few miles.

No good news I'm afraid.

The garage looked at my car this morning with a cold engine, it was misfiring.

They think it's most likely an injector but with no fault codes, they don't know which one.

So back to square 1.

To replace all 4 injectors would cost around £2000.00, so I would rather just replace the faulty one.

Find a garage who can test each injector on rig to locate faulty one.

What do you think of diesel addatives that claim to clean your injectors.Do they work?

On 10/10/2025 at 17:11, johnkitchen said:

No good news I'm afraid.

The garage looked at my car this morning with a cold engine, it was misfiring.

They think it's most likely an injector but with no fault codes, they don't know which one.

So back to square 1.

To replace all 4 injectors would cost around £2000.00, so I would rather just replace the faulty one.

It's about £30 to test each injector plus removal & refitting.

If an injector is faulty, why would it sort itself out after a few miles?

On 17/10/2025 at 00:57, ords said:

If an injector is faulty, why would it sort itself out after a few miles?

As the engine warms up combustion is easier, hence longer glow plug function on colder days.

Well my Skoda still runs rough when cold and there is no fault code.

Could it possibly be a faulty coolant sensor which thinks that the engine is hot when it's actually cold?

12 hours ago, johnkitchen said:

Well my Skoda still runs rough when cold and there is no fault code.

Could it possibly be a faulty coolant sensor which thinks that the engine is hot when it's actually cold?

Anything is possible. If that was the case, you would get a fault code. Can you find somebody who has an ODBEleven and get a proper VAG codescan done on the car please?

I have just put a bottle of Wynn's Gold Diesel treatment in the tank.

To my total amazement the car is running normally again from cold.

What a great product.

It's probably worth running your car on Super Diesel or using a Cetane improver to keep your engine in best fettle.

On my last 5 VAG diesels, I’ve been using this every time I refuel. Never had an issue with running rough. It slightly increase mpg as it increases cetane level by 4. I never overdose and in summer underdone by about 25%. Not cheap of course, far from expensive with the added mpg

I normally buy a few at a time when on offer.

Millers Oils 6204KB Diesel Power Ecomax Fuel Treatment 500ml

John

Edited 14 November, 202514 Nov by Trickiejohn