Hi all, my 1.2 tsi isnt running the best, in higher gears and higher rpm the engine hesitates a bit and the idle feels like it could be a bit better, there is no check engine light or something.
It has new spark plugs, new spark plugs wires, new air filter and new throttle body (when replacing the spark plugs it looked like they were running a little lean)

Before I replace the coil pack I decided to check for vacuum leaks and I saw this line super cracked and more lines going to the brake booster to be cracked also.
Can I replace them with rubber lines? these ones are rock hard.

Clean up those areas, cover with plenty of tape and see if it makes any difference to engine running.

Sons 1.2htp mk1 is the same. Cracked everywhere. His idle was all over the place. Taped up and been fine since. Did think of replacing with rubber vaccum hose but not sure why these are rigid in the first place.

Alasdair

Rigid plastic hoses can't collapse under vacuum when they get old and perished.

They just crack and leak at the terminations instead. ☹️

4 minutes ago, Breezy_Pete said:

Rigid plastic hoses can't collapse under vacuum when they get old and perished.

That makes sense. On my old volvo they were reinforced rubber but seems that more modern cars are rigid. Pity as reinforced rubber seems a lot cheaper than buying a replacement rigid one.

Alasdair

2 hours ago, Breezy_Pete said:

Clean up those areas, cover with plenty of tape and see if it makes any difference to engine running.

It is usually felt in 6th gear when accelerating at 2000+- rpm at the highway entrance on my daily commute to work so tomorrow I will give an update.

1 hour ago, Breezy_Pete said:

Rigid plastic hoses can't collapse under vacuum when they get old and perished.

They just crack and leak at the terminations instead. ☹️

I also have a 1993 Skoda Favorit (carbureted) and its rubber vacuum lines are so easy to deal with, I hate new stuff 😒.

That's a car you don't see very often. Cant say I have seen one in at least 20years. Used to be a bright yellow pickup version around Inverness about 15 year ago and I think an old 110R but only seen in summer. Those were the days where cars were fairly simple.

Alasdair

2 minutes ago, Alasdair1 said:

That's a car you don't see very often. Cant say I have seen one in at least 20 years. Used to be a bright yellow pickup version around Inverness about 15 year ago and I think an old 110R but only seen in summer. Those were the days where cars were fairly simple.

Alasdair

I love that car, so simple and easy to service and very fun to drive, like a big go kart.

I bought it a few years ago from an old lady that bought it brand new, Too bad the rust is slowly taking over.

Same up here in Inverness. Far to much salt on roads hence why you only see proper cars in the summer. I have a Mk1 mazda eunos(mx5 jap import) that is in pretty good condition so hope to have it on road this year. Daughter has a 1.6 gti peugeot 205 plus she is working on a classic mini. Thing should go like a rocket. It as a metro 1300 engine with loads of extras etc.

Alasdair

5 hours ago, OmerGarabagi said:

Can I replace them with rubber lines? these ones are rock hard.

I'd be for just cutting off the split ends and sleeve it with rubber hose. Vacuum hose is specific but for the amount you'd need to sleeve the ends I doubt it'd matter.

On 28/03/2026 at 10:38, Breezy_Pete said:

Clean up those areas, cover with plenty of tape and see if it makes any difference to engine running.

Well it didnt seem to make a difference.

Thinking on replacing the ignition coil because the engine hesitation feels like a random misfire on load.

It just doesnt explain why my old spark plugs look like they were running lean.

33 minutes ago, OmerGarabagi said:

Well it didnt seem to make a difference.

I thought you mind find that.

Safer for the brake assist system with it all taped up anyway though. 🙂

There could be a few other reasons for hesitation, but ignition system is a good thing to rule out relatively cheaply.

Maybe coil pack is failing at high revs or cam sensor. Have read that a bad cam sensor sometimes wont create a code. Was it doing it before plug change?

Alasdair

6 hours ago, Alasdair1 said:

Maybe coil pack is failing at high revs or cam sensor. Have read that a bad cam sensor sometimes wont create a code. Was it doing it before plug change?

Alasdair

Yes, I changed the plugs and wires to try and solve this.

I will take a look at the camshaft sensor, clean it and see if it makes a difference.

The less money I spend the better 😅.

Thanks.

So I cleaned the camshaft sensor with electronic cleaner spray, I also replaced the ignition coil pack, and nothing has changed.

Maybe I need to check for vacuum leaks in the air intake, the old plugs were probably telling the truth.

On 29/03/2026 at 22:34, Breezy_Pete said:

I thought you mind find that.

Safer for the brake assist system with it all taped up anyway though. 🙂

There could be a few other reasons for hesitation, but ignition system is a good thing to rule out relatively cheaply.

So I did a homemade vacuum leak test, used a vape instead of a smoke machine (removed 2 years from my lungs) and I found that there is a quite big leak from a hose connector going to the brake booster (lower red circle in my first image) that I tried to tape but I probably didnt do a good job.

So I need to replace that hose and maybe (I hope) it was the cause of these issues I was having.

Well done. 🙂