Boost / vacuum issue 850r 1996

DuncanLT · Post by **DuncanLT** » 17 Jul 2026, 05:34

Ino another boost post but im still unsure.

Issue - boost / vacuum pressure is different every time I get in my car, sometimes it's perfect and will sit un vacuum '10 o'clock position' and will boost all the way up to the '2 o'clock postion' and then the next day it will hardly be in vacuum and then hardly boost.

What I've done - changed all hoses connected to the TCV and also changed the turbo bypass valve. Both of these changed seem to have give me slightly more boost / vacuum but it is still even inconsistent/ different every time I get into my car.

I was thinking this is a TCV issue? If so should I get an OEM or is there a company which sell an aftermarket one which is perfectly fine.

Thanks,
Duncan

Post by **scot850** » 17 Jul 2026, 08:43

Definitely sounds like a TCV or hose fitment leak. I would tend to the TCV being the issue as it is inconsistant.

Neil.

Post by **BlackBart** » 17 Jul 2026, 20:19

It wouldn’t be the big intercooler hoses, would it?

Post by **abscate** » 18 Jul 2026, 02:43

BlackBart wrote: 17 Jul 2026, 20:19 It wouldn’t be the big intercooler hoses, would it?

Absolutely worth checking.

This means removing each one, and inspecting for splits and cracks.

Looking at them on the car is useless.

A smoke test is the best you can do on the car. Protect the MAF from smoke