Subaru IMPREZA 2004 Service Manual page 187

TROUBLE
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.> or
<Ref. to EN(H4SOw/oOBD)(diag)-2, Basic Diagnostic Procedure.>
Intake system
Fuel line
Belt
Compression
Lubrication system
Cooling system
Others
ME(H4SO)-91
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 plugs or defective gasket
Loosened cylinder head bolts or defective gasket
Improper valve seating
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
Overheating
Malfunction of evaporative emission control system
Stuck or damaged throttle valve
Accelerator cable out of adjustment
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
C