MerCruiser 305 CID (5.0L) Service Manual page 618

SERVICE MANUAL NUMBER 24
Rough, Unstable, or Incorrect Idle, Stalling Symptom
Step
Definition: Engine runs unevenly at idle. If severe, the engine or vessel may shake.
Engine idle speed may vary in rpm. Either condition may be severe enough to stall
the engine.
1
2
3
4
5
6
7
8
Index
90-861327--1 OCTOBER 1999
Action
Was the "On-Board Diagnostic" (OBD)
System Check performed?
Was visual/physical check performed?
1. Check for proper operation of the IAC
valve.
• Refer to Table A-8 in "General System
Diagnostics" section.
Was a problem found?
1. Check for proper operation of Ignition Con-
trol (IC) circuit and the Knock Sensor (KS)
circuit.
Was a problem found?
1. Check integrity of the primary and second-
ary wiring.
2. Check routing of the wiring.
3. Check condition of IC module, pick-up coil,
distributor cap, rotor and spark plug wires.
Was a problem found?
1. Check ignition coil for cracks or carbon
tracking.
Were cracks or carbon tracks found?
1. Remove spark plugs, check for wet plugs,
cracks, wear, improper gap, burned elec-
trodes or heavy deposits.
• Refer to Distributor Ignition System.
NOTE: If park plugs are gas or oil fouled, the
cause of the fouling must be determined before
replacing the spark plugs.
Were spark plugs damaged?
1. Check the injector connections. Correct as
necessary.
Was a problem found?
FUEL INJECTION SYSTEM TROUBLESHOOTING
Yes
PROCEED TO
Step 2
Visual/ Physical
Step 3
OBD
No
OBD
Check
Step 4
Step 5
Step 6
Step 7
Step 8
Step 9
Page 5F-17