Subaru 2004 LEGACY Service Manual page 197

ENGINE (DIAGNOSTICS)
Symptom
6. Surging
7. Spark knock
8. After burning in exhaust system
*1: Check ignition coil & ignitor ASSY and spark plug.
*2: Indicate the symptom occurring only in cold temperatures.
*3: Ensure the secure installation.
*4: Check the fuel injector and fuel pressure regulator.
*5: Inspect air leak in air intake system.
General Diagnostic Table
Problem parts
1) Mass air flow and intake air temperature sensor
2) Manifold absolute pressure sensor
3) Engine coolant temperature sensor (*2)
4) Crankshaft position sensor (*3)
5) Camshaft position sensor (*3)
6) Fuel injection parts (*4)
7) Electronic throttle control
8) Fuel pump and fuel pump relay
9) EGR valve
1) Mass air flow and intake air temperature sensor
2) Manifold absolute pressure sensor
3) Engine coolant temperature sensor
4) Knock sensor
5) Fuel injection parts (*4)
6) Fuel pump and fuel pump relay
7) EGR valve
1) Mass air flow and intake air temperature sensor
2) Manifold absolute pressure sensor
3) Engine coolant temperature sensor (*2)
4) Fuel injection parts (*4)
5) Fuel pump and fuel pump relay
EN(H6DO)(diag)-266