Idle hum and vibration 1.5tsi

[Shenbu]

Hi, I am new here thought I would ask a question and round up some answers before trying anything extreme.

I am a driving instructor so want to make sure the car is right and doesn't let me down.

I have a 2020 1.5tsi 150 FR 42k miles

Today on a lesson I noticed when we pulled over to discuss lesson plan the car at idle had a distinctive extra hum and vibration when idle. The engine is so quiet and smooth most pupils turn the car off when it is on as they think the engine isn't running which is always funny.

Best way I can describe it is car is normally: mmmmmmmmm. But today it is mmmmMmmmmMmmmmM (bet you mechanics love customers describing the sounds).

So from my investigations I don't think it is hunting as the revs are stationary at 1k rpm. Didn't notice it when I set off on a cold start to need to do that. Car was taken on 60 roads to get to pupil so had time to warm up. Temp today is 9 degrees.

It's due a service on the 11/11/2023 (it's past due tbh but garage couldn't get an earlier timeslot) I will be getting an oil change, oil filter and air filter change (it's my last service with the garage so it's included). I will personally be changing the pollen filter and was thinking of doing the spark plugs (friend is a mechanic he suggested this forum) as I don't want to pay extra to the garage for that work.

Sort of hoping the oil change fixes it, if not the spark plugs, if not then walnut blasting. I really don't want to deal with the Dealership as I have nothing but issues with them in the past taking over 3 months to fix 1 issue, 3 months for another (car was useable) both accounts took the car in and they didn't even attempt fix the issue so that's 2 extra wasted days plus taking it back to actually get fixed. Also warranty ran out 2 months ago.

Just read it might be alternator/battery related, car is stalled a lot by the learners so hopefully it's not that as it uses the stop start a lot.

Thank you

 

[Alex667]

When I’ve had similar before (on an Astra), it was the PCV valve on the valve cover that was buggered, although that was accompanied by the revs dipping 50-100rpm each time it happened.

 

[BoomerBoom]

Dealership is unlikely to be any help, unless it's coming up as an error code or the broken part is hanging off, they will be happy to charge you to investigate it though.

With a driving school car it's possible your students have loosened something, somewhere on, in, or underneath the car - that is now vibrating with a harmonic?

 

[Shenbu]

Dealership is unlikely to be any help, unless it's coming up as an error code or the broken part is hanging off, they will be happy to charge you to investigate it though.

With a driving school car it's possible your students have loosened something, somewhere on, in, or underneath the car - that is now vibrating with a harmonic?

Sorry I totally forgot about this post - Been so busy with tests and Christmas.

Car is in the garage today and going to collect it in 30 mins.

Nothing is loose, the entire car shakes - Sometimes you can see the engine trying to rattle out of the mount it vibrates that badly sometimes (I had the bonnet open to show a friend).

It feels like a misfire.

So the dealership has done exactly what you said, no fault has come up so there isn't anything they can find to fix, so according to them all working normally.

In December the tech wanted to compare the misfires after 2 weeks - All of them around 300 recorded misfires apart from cylinder 2 which was over 1000. I am also now getting worse mpg from the car.

I suspect it's a dodgy spark plug, but unless they can narrow it down they don't want to do any work on it that would cost unless they are 100% sure it's that.

I hate how it vibrates the whole car and I have to explain it's ok don't worry, sometimes is barely noticeable other times it feels like someone is choking and grunts, as I said, the whole car shakes . But my biggest concern that this small issue is going to lead up to a bigger issue later down the line.