VW Mk5 Golf GTi (TFSI) Misfire When Engine Is Warm

This post summarised for anyone in a rush...

  • 2005 VW MK5 Golf GTI 2.0 (AXX engine)

  • Slight misfire on idle when engine is warm
  • No symptoms when engine is cold

  • New coil pack for cylinder 1

More information

I recently sold my 2005 Honda Civic Type R (EP3) and bought a 2005 VW Mk5 GTI in the hope of moving to something a little more torque-y and refined.

I was going through that first month or so of owning a new used car which I hate with a passion. You know, when you're constantly thinking:
  • Have I bought a lemon?
  • Was that a knock?
  • Is that sound normal?
  • Is the engine going to explode
Well anyway, during that enjoyable period I noticed that when the car was up to temperature it would slightly stumble occasionally on idle, most "non-car" people wouldn't have noticed it, but anyone into their motors would.

I did not experience any hesitation or loss of power, but after scaring myself with stories of compression loss and head gasket failure I decided the first sensible option would be to change the coil packs and spark plugs.

So I ordered the following parts:
  • Genuine VW coilpack - 07K 905 715 G (previous revision 07K905715F)
  • Bosch spark plug - 101 905 631 H (Bosch part number: FR5KPP332S)
Before I had a chance to fit these the misfire got much worse and finally conked out and wouldn't run at all.

Luckily I had an OBDII bluetooth adapter and Torque for Android which enabled me to read the OBDII fault codes to get a better idea of what was going on.

OBD Scan Result: 
  • P0300 - Random/Multiple Cylinder Misfire Detected
  • P0301 - Cylinder 1 Misfire Detected
  • P0302 - Cylinder 2 Misfire Detected
  • P0351 - Ignition Coil A Primary/Secondary Circuit
Coil A = Cylinder 1 so at least that seemed consistent. However, still not conclusive that this is a coil or spark plug issue.

I changed the spark plugs first but this made no difference. The old plugs and coils were pretty filthy though with lots of corrosion build up pretty much everywhere where you don't want corrosion build up.
bad bosch spark plugs from golf mk5 gti

After changing the coil pack on cylinder 1 the engine fired straight up and the misfire disappeared.

Problem solved.

Cleaning Cloudy/Foggy Car Headlights With Bar Keepers Friend

before and after cloudy headightsCloudy car headlights not only look bad, but they are also dangerous for two reasons:
  1. Reduces the amount of light which makes it out of the headlights and onto the road, where you want it.
  2. It impairs the all important scattering of the beam, causing glare for other road users.
It is possible to fail an MOT for cloudy headlights as it ruins the light scattering. A local garage tried to charge us £60 just to clean our cloudy headlights so it's well worth looking at alternative methods and doing it yourself!

There are many ways of cleaning headlights which have gone foggy and using Bar Keepers Friend is just one of them which I have used with good success so I thought I would share.

Bar Keepers Friend vs. Brite Powder Power

To avoid confusion from my photos, Bar Keepers Friend recently re-branded to Brite Powder Power, so they are exactly the same product, just a different label.

Bar Keepers Friend is a more familiar brand which has been around for quite a while and has many uses around the home including cleaning kitchen pans, toilets and as covered in one of our previous posts, it is also excellent at cleaning car windscreens.

How to clean your headlights

Cleaning cloudy car headlights with Bar Keepers Friend (Brite Powder Power) is very quick and easy and in a few minutes you will have lovely clear headlight lenses again.

The advantage of using this method to restore headlights instead of wet sanding them is that Bar Keepers Friend does not scuff up the lenses so much that you need to polish them back clear again.

For really badly cloudy headlights it may not be enough but for the price of Bar Keepers Friend on Amazon (£3.10 with Free Delivery) it's certainly worth a go.


  • Polishing pad or cloth
  • Bucket of water
  • Bar Keepers Friend

Step-by-step guide

Step 1. Lightly wash the headlights and surrounding area with the polishing cloth and water
This is just to remove any grit which might be sitting on the headlights. Even though the plastic used in headlights is generally very hard-wearing, you don't want to risk accidentally creating scratches in the lenses or paintwork around the headlights when you rub in the Bar Keepers Friend.

Step 2. Pour a small amount of the Bar Keepers Friend onto the damp polishing pad and work into the headlight lens. The moisture from the polishing pad will turn the powder into an abrasive paste and you should be able to feel that it is rough against the headlight lens.

You should apply a good amount of pressure and polish in a circular motion being very careful to avoid touching the paintwork as this could mark your paint.

Depending on how badly fogged your headlights are this could take up to 15 minutes of constant polishing for each headlight and you will need to re-apply the powder to the polishing cloth every couple of minutes. Who said saving money would be easy?

Step 3. Once you are satisfied that the headlights have been restored then you need to gently wash all the powder residue from around the headlights and bodywork. This is easily done with some water and sponge.

Step 4. Stand back and admire you restored car headlights.

Tried this out and impressed (or unimpressed) with the results? Please leave your comments below.

restored car headlights

Why does my car squeal?

If you are wondering why your car is making a squealing noise then this quick guide should help you find the cause of the squeal. Don't let it annoy you any longer...

99% of high pitched squealing noises from cars are likely to be caused by either:
  1. Fan belt
  2. Brakes
Identify the cause of the squeal
When the engine is cold and the car is parked, open the bonnet and then start the engine. The fan belt is often located on the left side of the engine and you should be able to see it moving when the engine is running.

Listen for noise coming from this area, particularly when the belt is under extra load.

You can put extra load on the fan belt in a few different ways depending on your particular model of car:
  • Increase the engine revs
  • Put the alternator under load e.g. turn on full beam headlights, heated rear windscreen etc.
  • Turn on the air conditioning
  • Turn the steering wheel to full lock and then back again
Cars most often squeal after the car has been left overnight, particularly if it is damp - this is because the alternator is putting extra load on the belt as it's trying to re-charge the battery and also dampness can reduce grip, causing the belt to slip.

If you can hear the squealing noise when the car is stationary, then the problem is probably your fan belt (also known as alternator belt, aux belt or accessory belt) and you should check out our guide on how to fix it.

A worn fan belt on a Honda Civic Type R
If you cannot hear the squeal noise when the car is parked with the engine running then it is quite likely that the noise is related to your brakes. Go for a drive with the windows down and determine if it happens when you are driving or only under braking.

Unless you have a seized brake caliper then any squealing is only going to occur when you apply the brakes to slow down. If you car squeals when you apply the brakes then I would strongly recommend taking it to a professional.

How to Solve That Squeaky Fan Belt Noise

squeaky fan belt noise
A worn fan belt on a Honda Civic Type R
Fed up of that annoying squeal from your fan belt every time you start the car? Yep me to. That's why I wrote this article.

Luckily, the most common cause of squealing is the auxiliary belt/fan belt which can normally be fixed relatively easily by the home mechanic, the good news is that even if you do have to take the car to a garage, the cost is likely to be low. Before calling a garage, make sure you read our blog post all about the causes of squeaky/squealing fan belts and how you might be able to fix the problem by yourself for free!

Fan belt vs alternator belt vs auxiliary belt vs serpentine belt vs vs accessory belt
Confusing eh? 99% of the time these terms are all referring to the same thing, which is a belt powered by the engine to drive auxiliary components such as the cooling fan, alternator, power steering pump or air conditioning compressor.

To minimise confusion, for the rest of this article I will refer to this belt as the 'fan belt'. One because that's what most people still tend to call it, and two because it's quicker to type. ;-)

Why does the fan belt squeal?
The squeal/squeak noise is caused by the fan belt slipping on the pulleys. There are several possible reasons for why this happens.

When electrical load is applied to the alternator (e.g. turning the steering wheel in a car with electric power assisted steering) it takes more force to turn and so there is a greater amount of friction the fan belt must overcome to turn which makes it more likely to slip.

Fan belts are designed with V shaped grooves which run the entire length of the belt. This allows the belt to slip a certain amount, this is because the load on the accessories driven by the fan belt can suddenly increase, and without this ability to slip then they would likely snap.

You are more likely to hear that annoying squeaky noise on damp mornings if the car has been left overnight. This is because the dampness can cause the belt to have less grip and also because if it's cold, the alternator will have more load on it.

Five possible causes:
  1. Worn fan belt
  2. Incorrect fan belt tension
  3. Oil leak in engine bay
  4. Seized components driven by the belt
  5. Pulleys/components are out of alignment

1. Worn fan belt
Fan belts are made with rubbers which degrade and glaze over time. Moisture, oil and heat cycles all contribute to this process and once the belt is glazed it is more likely to slip and cause that annoying squeal sound.

2. Incorrect fan belt tension
Quite simply, if the belt is too lose it will 'slip' on the pulleys which will cause that annoying high pitched squealing noise.

A crude way to test the tension of the belt is to press on the belt between two pulleys with your thumb - you should get about 1/2 inch of deflection. This should give you a rough idea of whether your fan belt is tensioned correctly.

Depending on what car you have, the tension of the fan belt will either be set manually or by an auto adjusting tensioner.

If the tension can be manually adjusted then refer to a Haynes manual or similar to find out how to carry out this procedure.

If your engine uses auto adjusting tensioners then these should be replaced along with the fan belt.

3. Oil leak in engine bay
If your fan belt belt or the various pulleys which it runs through become contaminated with oil, even just a fine mist coating, this will reduce the grip the belt has and will cause it to slip and squeal more than usual.

Oil leaks in the engine bay are more likely to occur on engines with a turbo because any small leaks in the intake system or intercooler pipework (which are under pressure on boost) are likely to spray fine droplets of oil all over your engine bay.

To rectify this problem you need to find and fix the oil leak (which can be easier said than done) and then replace the fan belt being sure to also clean any pullies, tensioners and guides to remove any oil residue.

I have also heard of 'other fluids' such as power steering fluid or coolant causing belts to slip so it is worth checking for leaks from the reservoir as well.

4. Seized components driven by the belt
If the alternator bearings or any of the pulleys are seized/sticky then this could cause the belt to slip simply because it is creating more drag than the belt can handle.

5. Pulleys out of alignment
If the belt guides are out of alignment the belt cannot sit properly and will cause a noise. Normally, fan belt noises which are caused by misalignment of the pulleys will be more of a chirping noise than a squeal.

Before spending money on new belts or professionals, the cheapest and easiest thing to try is cleaning the belt and pulleys with carb cleaner or even a mild detergent mix. In some cases the slipping belt is caused by contamination from oil or other fluids from the engine bay and simply cleaning this off will stop the noise. In any case cleaning the belt and pulleys should help increase friction slipping and causing that irritating squeaking sound.

One diagnosis method is to spray a bit of water on the ribbed side of the belt when the engine is running and making the noise. If the noise stops then this is likely cause by an alignment issue. If the noise gets worse then it is likely a friction issue.

Please feel free to leave any comments or tips you might have for other readers below.