CO
Normal
Low
High
High
High
4
HC
Problems
High
Rough idle
Rough idle
Rough idle
(Black smoke
from exhaust
pipe)
1. Fault
. Incorrect ignition timing
. Fouled, shorted or improperly clearance of spark plug
2. Incorrect valve clearance
3. Leaky intake & exhaust valves
4. Leaky cylinders
1. Air leaks
. PCV hoses, intake manifold
. Throttle body
. Brake booster circuit
2. Lean mixture gas causing misfire
1. Clogged air filter
2. Clogged PCV valve
. Faulty ECU
. Faulty fuel pressure regulator
. Faulty water temperature sensor
. Faulty air compressor
. Faulty injectors
. Faulty throttle position sensor
Causes
Table 3