1.4 8v noticeable blowby from oil filler

I can feel very noticeable blowby from the oil filler. I am using the push on oil cap and it has not blown off. When I place the cap near it's almost like it's being sucked and pushed at different times.

The breather pipe is clear, although this is not a valved system, just a straight pipe from the rocker cover to the throttle body intake. Plugged into VAG-COM shareware version and this said misfire on cylinder 1. Have since replaced the spark plugs and cylinder 1 plug had worn to have the biggest gap, so think that explains that code.

Oh and I used a flushing oil (rather than flushing additive) when I changed the oil recently.

Is this normal? Is it likely to be indicative of any problems? Thanks in advance.

Edited 4 March, 201016 yr by anewman