For 1990-2009 cars

Condition | Action
--- | ---
Important: Oil in the turbocharger air inlet duct, oil on the compressor wheel, and oil throughout the charge air cooler system is normal with a closed PCV system. Do not attempt repairs for this condition.
Restricted air system | Inspect for clogged air filter element or restricted air inlet system.
Restricted exhaust system | Inspect for a restricted exhaust.
Leaking exhaust system | Inspect for exhaust manifold leaks.
Poor oil drainage from turbocharger | Inspect for restricted turbocharger oil drain pipe.
Restricted crankcase ventilation system | Inspect for restricted crankcase ventilation system.
Worn internal engine components | Inspect for excessive blowby or engine oil consumption.