1st.. The missing link is a 1 way check valve. they do go bad, and if that were the case, it would case issues like you are having.

2nd, A check valve is a Hack, And I know you may be on a budget, but what will that budget look like if you damage your motor because you cut a few corners?

You can pick up a 2-3bar map these days for pretty cheap and then have you OEM ecu modded to give you the ability to fully tune you car(crome) for little more. you dont have to spend alot to get alot. you just need to know where to spend you money on what

I dont condone this. but if you REALLY need a new check valve, LMK what year you motor is, . I may have 1 for you in stock brand new in that package(the real Missing Link) not a knock-off brand. LMK if I can help.......