1st guess is a vacuum leak, a crack in a hose.
Can you do a boost leak test ?
Use a pint size paint can to plug the big hose off the air filter box, witha air compressor give ashort blast of air into the small line off the BOV then put you thumb over the hose, listen for leaks.
199,000 May 12 new ej257 short block, Aug 11 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. CHECK your oil, these cars use it.
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