Engine Performance & Diagnostics Flashcards

A 2.0T TSI shows long-term fuel trim at +18% at idle that drops to +3% at 3,000 rpm. What is the most likely cause?

Answer: An unmetered vacuum leak

A vacuum leak has the biggest effect at idle, when total airflow is low, and matters less as airflow rises.

On a VW with a P0302 misfire, the technician swaps the cylinder 2 ignition coil with cylinder 3 and the code changes to P0303. What is the next step?

Answer: Replace the ignition coil that moved

The misfire followed the coil, so the coil is the faulty part.

In VW component naming, what does G62 refer to?

Answer: Coolant temperature sensor

G62 is VW's designation for the engine coolant temperature sensor.

Why are VW direct-injection (TSI/FSI) engines prone to carbon buildup on the intake valves?

Answer: Fuel is sprayed into the cylinder, so it never washes the backs of the intake valves

Port injection washes the valves with fuel, but direct injection skips the intake port, so oil vapor deposits build up.

A leak-down test on one cylinder shows air escaping from the oil filler neck. What does this indicate?

Answer: Worn piston rings or cylinder wall

Air reaching the crankcase means it is getting past the piston rings.

A 1.8T or 2.0T TSI sets P0299 (turbo underboost) and has a whooshing noise under load. Which part should be checked first?

Answer: Diverter valve (N249/recirculation valve) diaphragm

A torn diverter valve diaphragm lets boost escape back to the intake, which causes underboost.

After replacing or cleaning the electronic throttle body on a VW, what should be done?

Answer: Perform a throttle body adaptation in Basic Settings

The ECM must relearn the throttle valve's end stops through a Basic Settings adaptation.