The 1.8T's vacuum plumbing — the N249 valve, diverter valve, check valves and the SAI/PCV lines — is a spaghetti of small hoses that perish and leak with age, giving you boost loss, rough idle and fault codes. A popular, cheap job on any older 1.8T is to refresh and simplify it. See 1.8T 20V Engine Family and 1.8T Coil Packs Sludge
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