Mk4 GTI 1.8t Running Lumpy

[Dancarr43]

Hi everyone! I really need some advice! My 1.8t gti has begun running lumpy when the engine has warmed up in low revs! 2 garages don't have a clue what's wrong as there is no warning light on the dash, and oxygen sensor and crankshaft sensor has been ruled out. It first occurred while sitting at 80 on the motorway, it began losing speed and struggling to tick over when I hit traffic. I parked up and the next day it was running fine, then same again! Is this an oxygen leak from somewhere? I know the engine is in great condition, with full service history and recently had the water pump/timing belt changed. Any suggestions would be welcome as I may have to get rid of my beloved mk4 😔 Thank you!

[Dancarr43]

It's also worth mentioning that the noise seems to be coming from the bottom of the engine when warmed up and ticking over

[lemski]

Vac pipes been checked? If they split or leak air it makes 1.8t do strange things

[Dancarr43]

This sounds like a very good shout! I'll get them checked, thank you so much!!

[gazareth]

what kind of noise are you hearing?

[Dancarr43]

Hi everyone, thank you for all your help! It turns out it was the vac pipes, once I took the oil filler cap off it was spluttering out of there and was clear it was a breathing problem. The GTi is now back on form, thank you all so much for your help! All the best!