A turbocharged vehicle lacks power. Probing the intake system, you find thick oil coating the inside of the intercooler and intake manifold. What is the most likely cause?

1. A leaking turbocharger compressor shaft oil seal or a restricted turbocharger oil return line
2. The engine oil filter bypass valve is stuck open
3. An excessive amount of coolant entering the intake manifold
4. The fuel pressure regulator is leaking fuel into the vacuum line