Hi guys, got an issue with my daughters Bora equipped with a 1.6 petrol code BCB. At idle it suddenly started cycling between normal rpm and about 500, never actually cutting out. Long story short, cleaned the throttle body and did a throttle body alignment and all seemed to be ok. Until... I noticed that removing the oil filler cap caused the idle to increase. Were these two related? Seems that when the diaphragm fails it can pull a big vacuum in the crankcase and subsequently allow unmetered air into the intake manifold after the throttle, so I now suspect that to have happened. Before she splashes out on a new oil separator/POV at nearly 100 I thought Id ask if anyone else has seen this before. If the diaphragm was split then surely it would idle high all the time plus doing the tba process ought not have fixed it yet it appears to have - so far.

Any thoughts?