Seriously stuck with a weird issue

[danny1204]

Hey all, posted last week about a map sensor issue which since has been tested for a vacuum leak. Have sorted the main culprit pipe that leads from brake master cylinder to the intake but still having a nightmare trying to pi point the problem. Have has the intake, pcv and all the plumbing that goes to intake and throttle body off but have had no joy and even more codes been thrown up. Someone has said it may be a leak on the exhaust manifold or an o2 sensor but they've been replaced and from what I can gather are reading nominal. Am seeing a massive drop on kpa pressure in intake on map sensor when I give it some throttle. Can anyone help as am at my wits end with no visible problems occurring. Turns out I've got the bcb engine and there's **** all information on this anywhere