Subaru 2009 IMPREZA Service Manual page 319

Symptom
2. Rough idle and engine
stall
Engine Trouble in General
Problem parts etc.
Engine control system <Ref. to EN(H4SO)(diag)-2, Basic Diagnostic Procedure.>
Intake system
Fuel line
Timing belt
Compression
Lubrication system
Cooling system
Others
ME(H4SO)-101
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 fuel or insufficient fuel
Defective timing
Incorrect valve clearance
Loosened spark plug or defective gasket
Loosened cylinder head bolt or defective cylinder head
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
Defective rocker cover gasket
Over-heating
Evaporative emission control system malfunction
Stuck or damaged throttle valve
MECHANICAL
RANK
A
A
A
A
B
B
C
B
C
C
C
B
C
B
B
B
B
C
B
B
A
B
B
C
C
A
B