Weird Issue with my car making a humming juddering noise when idling

[Liam-James]

Hi guys I have a very weird issue with my Leon FR 2.0 TDI 2016, when the car is idling not all the time baring in mind but probably 90% of the time if I’m just stationary the car does a sort of juddering humming sound as though you are applying the tiniest amount of revs. The cars idling fine at aroun 750rpm the needle is dead still not moving at all but the cars doing a sort of juddering murmuring sound.

If I apply some revs and take it upto around 1000rpm I’ve then noticed the needle flickering up and down ever so slightly but then if I apply abit more revs upto around 12-1300 the needle is dead still again and the juddering stops, if I then release the accelerator and go back to idle the car is then juddering again but the needle is dead still and not flickering or moving.

While driving the car it is absolutely spot on and drives lovely and I have no issues, but I have noticed if I put the car into 1st or 2nd and release the clutch and just let it pull on it’s own using the toque it is a slight juddering motion and the car moves in a jerky motion.

I’ve also notice if I open the car door the juddering completely stops and will not start again at all until I shut the door. And also if I bang the heating or air con on full blast it stops but as soon as I turn it down a couple of notches the juddering then kicks in again, it’s the most annoying and weird thing I’ve ever noticed in a car and I’ve got no idea what could be causing it.

I’m praying that someone else has had this issue and can tell me what it is or if anyone has any idea because I really need to get this sorted.

Tha

 

[andylong]

It could be anything from an injector to any of the idle sensors or intake/vacuum issues.
Increasing engine load, will increase the fuelling required, suggest you look for a code or check all the injectors are functioning similarly.

 

[Liam-James]

It could be anything from an injector to any of the idle sensors or intake/vacuum issues.
Increasing engine load, will increase the fuelling required, suggest you look for a code or check all the injectors are functioning similarly.

So I took it to someone earlier who hooked it up and looked for fault codes etc and there wasn’t any coming up, but he connected his charging analyzer and looked at the battery for me and he believes it’s the alternator causing the issue. Because the voltage was constantly going up and down from 13 to 14 it wasn’t staying at constant voltage if that makes any sense, while he was connected to it it was just all over the place so his opinion is it’s the alternator but at this point I’m very confused and concerned about what it could be.

 

[andylong]

Yea the voltage should be steady at constant revs

 

[Liam-James]

Yea the voltage should be steady at constant revs

Looking like a I need a new alternator then, not sure how much that’s likely to set me back I’m probably best to get a brand new one rather than a used one from a breakers or eBay etc.

 

[andylong]

You may be able to buy just the regulator part

 

[andylong]

Also the regulator itself is usually quiet, investigate the unit for noise

 

[SteveGSXR600K1]

I sometimes feel a lumpyness at idle in my 184FR. I've changed my battery, but my Battery Monitor II never seems to show it gettting to 100% charged. Maybe two commutes a week of 24 miles each way isn't enough. I started to wonder if it was the alternator.

Best thing would be to find a independent VAG specialist. Anyone else would just start to chuck parts at the car until it's fixed.

 

[SuperV8]

I sometimes feel a lumpyness at idle in my 184FR. I've changed my battery, but my Battery Monitor II never seems to show it gettting to 100% charged. Maybe two commutes a week of 24 miles each way isn't enough. I started to wonder if it was the alternator.

Best thing would be to find a independent VAG specialist. Anyone else would just start to chuck parts at the car until it's fixed.

We have 'smart' charging systems/ alternators - which don't fully charge to 100% on purpose, to leave some headroom to store spare energy.
Cruising down a hill the volts will shoot up to 15-16v charging the battery fast, while under load the volts will reduce right down to 12 so its more efficient

When my battery was getting old I noticed this smart up and down voltage reverted back to steady alternator voltage something like 14.7 which can be a sign the AGM battery is getting 'tired'!

 

[SuperV8]

Looking like a I need a new alternator then, not sure how much that’s likely to set me back I’m probably best to get a brand new one rather than a used one from a breakers or eBay etc.

We have either Bosch or Valeo alternators. Looks like regulators are available. Example Bosch 0 272 220 854.

We also have one way clutches on the alternator pulley which can cause fluctuations if seized - easy to check - small screwdriver should be able to move the internal fan one way but not the other. If it can't move either way you need a new pulley.

Have a look at your alternator drive belt when idling - the tensioner should be still - if the tensioner is bouncing around this can be another sign that you have torque fluctuations. Turn off the AC to try to isolate to just the charging system.

 

[andylong]

We have 'smart' charging systems/ alternators - which don't fully charge to 100% on purpose, to leave some headroom to store spare energy.
Cruising down a hill the volts will shoot up to 15-16v charging the battery fast, while under load the volts will reduce right down to 12 so its more efficient

When my battery was getting old I noticed this smart up and down voltage reverted back to steady alternator voltage something like 14.7 which can be a sign the AGM battery is getting 'tired'!

The charging systems are only smart inasmuch as they vary the charge rate so the battery is not overcharged.
There's no reason to leave space for more charge in a starter battery.
A lead acid battery will not charge below 12.9 v ( this is because of the chemistry of the battery) and will charge up to its capacity, then gassing becomes a problem and the charge voltage must remain about 13.8v. More than that and it will begin gassing and killing your battery.
I'm unsure why the capacity of the battery matters to in car chargers, there seems no mechanism for this to matter to a charge system which seems be operating on voltage measurement alone. A fully charged lead acid is about 12.9v off load, after charging the voltage slowly drops to this.
Size only matters to rate of charge and this is dependant on voltage and the health of the battery.

 

[SuperV8]

The charging systems are only smart inasmuch as they vary the charge rate so the battery is not overcharged.
There's no reason to leave space for more charge in a starter battery.
A lead acid battery will not charge below 12.9 v ( this is because of the chemistry of the battery) and will charge up to its capacity, then gassing becomes a problem and the charge voltage must remain about 13.8v. More than that and it will begin gassing and killing your battery.
I'm unsure why the capacity of the battery matters to in car chargers, there seems no mechanism for this to matter to a charge system which seems be operating on voltage measurement alone. A fully charged lead acid is about 12.9v off load, after charging the voltage slowly drops to this.
Size only matters to rate of charge and this is dependant on voltage and the health of the battery.

This is a log of my battery voltage on my trip to work - you can see it varies from just over 13 - to just under 15 volts! This was on my old battery.
It's not doing this to stop the battery over charging!
It's doing this to try to save a little energy (improve MPG) - all these peaks in V are when i'm braking/slowing down - so it's charging the battery for free!
The battery needs a little space for this to work - which is why you never/rarely see the SOH reach 100%

This was a later log - as my battery was near 'retirement', the 'smart' function was disabled.

Interesting video regarding smart charging:
some manufactures are already above 15, 16 & 17volts when regen charging! and as low as 12.2v

 

[Liam-James]

Hi guys just a small update regarding this issue, the engine hunting as I now know it’s called I’ve realised it’s mainly doing it once the car is fully warmed up, so when I start the car in the morning for example it starts up perfectly, no engine hunt, no judder, I go for a drive and if I pull up at lights or just pull over to see what the engines doing it’s perfectly fine, but as the car warms up and it goes up on the temperature gauge by 1 bar at a time, it’s fine on 1, 2 & 3 bars but as soon as the temperature is on 4 bars at 90f that’s when the engine starts.

I didn’t quite realise this pattern but then the penny dropped yesterday as I was driving around and testing it, and that’s is when the engine hunt starts when the engine is upto temperature, it’s perfectly fine when it’s cold and warming up it runs like clockwork!

There has to be a cause for this and I can’t figure out why, and I can’t make sense why when I open one of the doors the engine hunt completely stops, or when I turn up the heating or AC full blast it stops but as soon as I turn it down or close the door the engine hunt kicks back in again. Its driving me completely insane at this point and I have no idea where to start!

It’s been on the diagnostic scanner and no errors are coming up so I’m at even more of a loss!

 

[moriarty]

If it's related to engine temperature could the noise be related to the fan? If the fan started pulling electrical load would it change the charging rate?

 

[Liam-James]

If it's related to engine temperature could the noise be related to the fan? If the fan started pulling electrical load would it change the charging rate?

I have absolutely no idea, but why when a door is opened it stop but when you shut the door it starts again?

How would I test to see if it is the fan?

 

[cupra14]

Watch the fuel trims as it does it - could easily be an air leak but this will tell you if it is or not, especially if the trims go saner when you rev gently.