Removing oil filler engine runs rough

[Howsafe Workwear and Safety Equipment]

Hi all

 

i am helping a young lad buy his first car - we went to look at a VW Polo 1.2 Match (petrol) on a 62 plate with 44k on the clock 

 

never come across this before but I took the oil filler cap off (engine running) and the engine started to run rough and almost stalled - is this normal or a fault ? 
 

submit your comedic best below 

 

thanks 

[TAFKARM]

It’s normal.

 

P.s miss you Clark xxx

[Jim RS]

Modern engines now have a pressurised system within the oil system so that any waste gases/fluids can be contained and recovered. All the metering etc. within the engine will be set for these pressure parameters and any leakage will affect these adjustments.

Along way round but yes removing the oil filler cap while engine is running will affect the normal operation.

[cast iron]

yep you've opened the crankcase up which runs under a small vacuum through the purge control valve to draw off the oil vapour

 

[Howsafe Workwear and Safety Equipment]

Much appreciated - thank you chaps 😀

[Howsafe Workwear and Safety Equipment]

On 22/11/2019 at 11:34, Meatibald Archpants said:

It’s normal.

 

P.s miss you Clark xxx

hi m8 - hopefully back on it this year - had a troublesome year at work with loads of investment but are getting there now 

 

miss you too 😘