Subaru Impreza 2004 Service Manual page 230

Symptom
6. Surge
7. Spark knock
8. After-burning in exhaust system
*1: Check ignition coil & ignitor assembly and spark plug.
*2: Indicate the symptom occurring only in cold temperatures.
*3: Ensure the secure installation.
*4: Check fuel injector, fuel pressure regulator and fuel filter.
*5: Inspect air leak in air intake system.
*6: Adjust accelerator cable.
General Diagnostic Table
Problem parts
1) Manifold absolute pressure sensor
2) Mass air flow and intake temperature sensor
3) Engine coolant temperature sensor (*2)
4) Crankshaft position sensor (*3)
5) Camshaft position sensor (*3)
6) Fuel injection parts (*4)
7) Throttle position sensor
8) Fuel pump and fuel pump relay
1) Manifold absolute pressure sensor
2) Mass air flow and intake temperature sensor
3) Engine coolant temperature sensor
4) Knock sensor
5) Fuel injection parts (*4)
6) Fuel pump and fuel pump relay
1) Manifold absolute pressure sensor
2) Mass air flow and intake temperature sensor
3) Engine coolant temperature sensor (*2)
4) Fuel injection parts (*4)
5) Fuel pump and fuel pump relay
EN(H4DOTC)(diag)-309
ENGINE (DIAGNOSTICS)