Hi guys,

So a friend of mine at the workplace has a Golf 4 GTI that is currently doing a tad over 300,000km's. The engine has never been opened before, and I must say that for its age the car goes really well.

So onto the problem:

When idling: The car has a clear miss below 3000rpm, over that and it sounds clean.

When driving: The car has an even bigger miss once load is applied, the miss is more apparent at WOT than POT. However, what is very strange is that the problem is there most of the time but clears out every now and then- in this case the car goes perfectly fine like it should. In 2nd gear @ POT, the car would surge from idle to about 3500rpm and if kept at POT- @ 4000rpm the miss would clear out and the car would go perfectly.

Things that have been changed: O2 sensor, N75 valve

What are the other possible things that could be looked at?

Good help is always appreciated.

8VALVE-zn wrote:Hi guys,

So a friend of mine at the workplace has a Golf 4 GTI that is currently doing a tad over 300,000km's. The engine has never been opened before, and I must say that for its age the car goes really well.

So onto the problem:

When idling: The car has a clear miss below 3000rpm, over that and it sounds clean.

When driving: The car has an even bigger miss once load is applied, the miss is more apparent at WOT than POT. However, what is very strange is that the problem is there most of the time but clears out every now and then- in this case the car goes perfectly fine like it should. In 2nd gear @ POT, the car would surge from idle to about 3500rpm and if kept at POT- @ 4000rpm the miss would clear out and the car would go perfectly.

Things that have been changed: O2 sensor, N75 valve

What are the other possible things that could be looked at?

Good help is always appreciated.

Does he or yourself have access to VCDS?

Sounds like maybe plugs could be gapped wrong or even a failing coil pack but I can't say for sure. If you have access to a scanner scan it for errors it's usually a good to start.

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8VALVE-zn wrote:Hi guys,

So a friend of mine at the workplace has a Golf 4 GTI that is currently doing a tad over 300,000km's. The engine has never been opened before, and I must say that for its age the car goes really well.

So onto the problem:

When idling: The car has a clear miss below 3000rpm, over that and it sounds clean.

When driving: The car has an even bigger miss once load is applied, the miss is more apparent at WOT than POT. However, what is very strange is that the problem is there most of the time but clears out every now and then- in this case the car goes perfectly fine like it should. In 2nd gear @ POT, the car would surge from idle to about 3500rpm and if kept at POT- @ 4000rpm the miss would clear out and the car would go perfectly.

Things that have been changed: O2 sensor, N75 valve

What are the other possible things that could be looked at?

Good help is always appreciated.

Does he or yourself have access to VCDS?

Sounds like maybe plugs could be gapped wrong or even a failing coil pack but I can't say for sure. If you have access to a scanner scan it for errors it's usually a good to start.

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Testing of the coilpacks will happen today.

The missing story is very very irritating because it could be anything really

Thanks for that!

AGU coilpacks are pretty robust and don't often fail like the other 20v turbo engines coils.
Any idea if there is software on the car?

The car is completely stock.

What's baffling is that the problem is only there every now and then.

The coilpacks have still not being tested, the coilpacks have been changed over the life of the vehicle (remember its on 300k km +).

There is a bit of a fuel smell coming into the car ever since the problem started.

Today it seems like the issue of missing is there even at POT, strangely tho if kept at POT and the engine is allowed to revv up past 4000rpm the issue some what clears up.

What else can be checked at this point?

Fuel or vacuum leak perhaps, check the injectors cups which are screwed into the intake manifold and see if they are leaking as you will easily spot if there's a leak. The injectors basically get seated in them.

Those parts fail over time I've had to replace mine as well.

Check the air/fuel ration on a dyno. If the thing goes lean under boost it will missfire as well. had quite few of them recently - the pumps are now at that age that they are starting to fail. The fact that it does it on WOT mostly can definitly point to a lean situation.

what are the apparent problems experienced with a bad N75 valve? And what are the symptoms of a bad N75?

A failed n75 would generally result in overboosting as it doesn't handle the boost pressure appropriately or it could result in no boost if it's somehow stuck open.

n75 stuck open will cause overboost. Stuck closed or have died will cause underboost or basically just wategate pressure which is 0.3 bar.
Closed is it's default valve - held there with a spring. activating the circuit opens the valve

Oh right, mixed those up..

Check if your fuel pump was replaced bud .

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Is the misfire only there on boost? Did you check for boost leaks? Also check your map sensor.


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