Thanks for your reply peter deffinetley something I will consider and eliminate if I can.

Which breather one way valve are you speaking of Tom? As I can remember the only breather pipe work in the manifold area are two plastic corrugated hoses going into either end of the cylinder head cover? It might be worth mentioning that this engine is naturally aspirated.

As I said i am aware that these engines apparently suffer with breather valve issues but would this not log "system lean fault codes" ?
Sorry if I seem argumentative but just trying to get my noodle around how these different faults which your all suggesting might affect the running, I'm more interested in learning through this job than fixing it now, although I will try my best
Thanks for the relies keep them coming!!

On a side note does anyone have any info on exactly how these breather systems actually operate? Spent about a month reading up on the PSA's but am all the wiser for it