Toyota MR2 1988 Repair Manual page 56

HC
co
High Normal
I
i
High Low
High High
ENGINE MECHANICAL - Engine Tune-up
EM-13
4. RACE ENGINE AT 2,500 RPM FOR APPROX. 90
SECONDS
5. INSERT HC/CO METER TESTING PROBE INTO
TAILPIPE AT LEAST
40
em (1.3 ft)
6. CHECK HC/CO CONCENTRATION AT IDLE
Wait at least one minute before measuring to allow the
concentration to stabilize, complete the measuring within
three minutes.
If the HC/CO concentration does not conform to regula-
tions, see the following for possible causes.
Troubleshooting
Problems Causes
1 . Faulty ignition:
• Incorrect timing
• Fouled, shorted or improperly gapped plugs
• Open or crossed high-tension cords
• Cracked distributor cap
Rough idle
2.
Incorrect valve clearance
3. Leaky EGR valve
4. Leaky intake and exhaust valves
5. Leaky cylinder
1. Vacuum leak:
• PCV hose
Rough idle
• EGR valve
• Intake manifold
( Fluctuating )
• Intake air control valve (4A-GE)
HC reading
• Throttle body
• Brake booster line
2. Lean mixture causing misfire
1 . Restricted air filter
2. Faulty EFI system
• Faulty pressure regulator
Rough idle
• Clogged fuel return line
• Defective water temp. sensor
( Black smoke )
• Defective air temp. sensor
from exhaust • Faulty ECU
• Faulty injector
• faulty cold start injector
• Faulty throttle position sensor
• Air flow meter