Subaru Legacy 2004 Service Manual page 315

Symptom
3. Low output, hesitation and
poor acceleration
4. Surging
Engine Trouble in General
Problem parts, etc.
Engine control system <Ref. to EN(H4SO 2.0)(diag)-2, Basic Diagnostic Procedure.>
Intake system
Fuel line
Belt
Compression
Lubrication system
Cooling system
Other
Engine control system <Ref. to EN(H4SO 2.0)(diag)-2, Basic Diagnostic Procedure.>
Intake system
Fuel line
Belt
Compression
Cooling system
Other
ME(H4SO 2.0)-85
Possible cause
Loosened or cracked intake duct
Loosened or cracked PCV hose
Loosened or cracked vacuum hose
Defective intake manifold gasket
Defective throttle body gasket
Defective PCV valve
Loosened oil filler cap
Dirty air cleaner element
Defective fuel pump and relay
Clogged fuel line
Lack of or insufficient fuel
Defective timing
Incorrect valve clearance
Loosened spark plug or defective gasket
Loosened cylinder head bolt or defective gasket
Improper valve sealing
Defective valve stem
Worn or broken valve spring
Worn or stuck piston rings, cylinder and piston
Incorrect valve timing
Improper engine oil (low viscosity)
Incorrect oil pressure
Over-heating
Over-cooling
Evaporative emission control system malfunction
Loosened or cracked intake duct
Loosened or cracked PCV hose
Loosened or cracked vacuum hose
Defective intake manifold gasket
Defective throttle body gasket
Defective PCV valve
Loosened oil filler cap
Dirty air cleaner element
Defective fuel pump and relay
Clogged fuel line
Lack of or insufficient fuel
Defective timing
Incorrect valve clearance
Loosened spark plug or defective gasket
Loosened cylinder head bolt or defective gasket
Improper valve sealing
Defective valve stem
Worn or broken valve spring
Worn or stuck piston rings, cylinder and piston
Incorrect valve timing
Improper engine oil (low viscosity)
Over-heating
Evaporative emission control system malfunction
MECHANICAL
RANK
A
A
A
B
B
B
B
B
A
B
B
C
B
B
B
B
B
C
B
C
A
B
B
C
C
A
A
A
A
A
B
B
B
B
B
B
B
C
B
B
C
C
C
C
C
C
A
B
B
C