Herb is right- an intake hose may only leak under power-car won't make boost in Park or Neutral.Your exhaust may be partially plugged if the catalytic converter is melted internally-check it by removing the "test" port plug just upstream of the cat.Check intake hoses first,though (it's easier)-the big one from the MAF sensor to the turbo intake tends to rot from the inside at the low point where blowby oil collects-remove hose to inspect! MAF failure may also cause your symptom-don't know for sure.The hoses are the first thing to check.
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