Sporadic low boost, AVCS / VVTI related?

[Sam86]

Hi, I’ve got a boosted gen 1 86 that makes 8psi on wastegate and 12 with boost controller.

Over the last month I’ve been stuck in intervals of being limited to 8psi for over 7 consecutive days and 200kms driven, only for the car to return to 12psi with no modification and make it consecutively for 4 days to then return to the 8psi cap which it’s stayed at since.

I had this issue to a lesser extent this time last year after my car was tuned. The tuner told me it was related to the AVCS not being active and that my boost would return after driving roughly 5kms and that the checking intervals don’t happen very often or last for long. That was relatively true at the time where it would return to full boost however it would usually only take a singular long drive and then wouldn’t return for months.


Really stumped on what it could be, car made full boost for months, only noticeable change was I installed a new compressor housing. Whilst the issue does coincide with the new housing being installed, very little was actually touched when changing it, and all those pipes were double checked and tightened, and then removed again and reinstalled when tightening alone didn’t fix the issue. All vaccum lines are secured and zip tied and the car was briefly making full boost without issue about a week after the housing was installed. Wastegate was checked and isn’t stuck open. Car builds boost and makes the power very quickly as it always has, it’s simply limited to 8psi now for whatever reason. It doesn’t feel laggy or like there’s something mechanically wrong

My tuner is extremely popular so it’s hard to speak to him to problem solve. Does this sound like a faulty vvti solanoid? Is there any way I can check to see if AVCS is engaging?

TLDR: boost being capped to wastegate, will randomly return to full boost with no changes or modification and then return to wastegate power after a few days. Boost solanoid, controller etc all under a year old. Checked all hoses/ clamps for boost leaks and can’t determine any, checked wastegate and seems to open/ close as normal
Maybe AVCS related?