Isuzu KB P190. Manual - part 501

6-4 ENGINE DIAGNOSIS (C24SE) 

Rough Engine Idling or Engine Stalling 

Condition Possible 

cause Correction 

Trouble in fuel injection system 

Idle air control valve defective 

Replace 

 

Throttle shutting off incomplete 

Correct or replace 

 

Throttle position sensor circuit 
open or shorted 

Correct or replace 

 

Fuel injector circuits open or 
shorted 

Correct or replace 

 

Fuel injectors damaged 

Replace 

 

Fuel pump relay defective 

Replace 

 

Manifold Absolute Pressure 
Sensor cable disconnected or 
broken 

Correct or replace 

 

Manifold Absolute Pressure 
Sensor defective 

Replace 

 

Engine Coolant Temperature 
Sensor cable disconnected or 
broken 

Correct or replace 

 

Engine Coolant Temperature 
Sensor defective 

Replace 

 

Intake Air Temperature sensor 
cable disconnected or broken 

Correct or replace 

 

Intake Air Temperature sensor 
defective 

Replace 

 

Knock Sensor (KS) circuits open 
or shorted 

Correct or replace 

 KS 

defective 

Replace 

 

KS Module circuits open or 
ground 

Correct or replace 

 

KS Module defective 

Replace 

 

Vehicle Speed Sensor circuit open 
or shorted 

Correct or replace 

 

Vehicle Speed Sensor defective 

Replace 

Trouble in emission control 
system 

Engine Control Module defective 

Replace 

 

Canister purge solenoid circuit 
open 

Correct 

 

Canister purge solenoid defective 

Replace 

 

Evaporative Emission Canister 
Purge control valve defective 

Replace 

 

Trouble in ignition system 

Refer to Hard Start 
Troubleshooting Guide 

Others 

Engine lacks compression 

Refer to Hard Start 
Troubleshooting Guide 

 

Valve incorrectly seated 

Lap valve 

 

Air Cleaner Filter clogged 

Replace filter element 

 

Valve timing incorrect 

Readjust 

 

Idle air control valve broken 

Replace 

 

ENGINE DIAGNOSIS (C24SE) 6-5 

Rough Engine Running 

Condition Possible 

cause Correction 

Engine misfires regularly 

Ignition coil layer shorted 

Replace 

 

Spark plugs fouling 

Clean or install hotter type plug 

 

Spark plug(s) insulator nose 
leaking 

Replace 

 

Spark plug wire incorrect 

Connect properly or replace 

 

Fuel injector(s) defective 

Replace 

 

Engine control module faulty 

Replace 

Engine knocks regularly 

Spark plugs running too hot 

Install colder type spark plugs 

 

Powertrain control module faulty 

Replace 

Engine lacks power 

Spark plugs fouled 

Clean 

 

Spark plug wire incorrect 

Connect properly or replace 

 

Fuel injectors defective 

Replace 

 

Manifold Absolute Pressure 
(MAP) 
Sensor or Manifold Absolute 
Pressure Sensor circuit defective 

Correct or replace 

 

Engine Coolant Temperature 
Sensor or Engine Coolant 
Temperature Sensor circuit 
defective 

Correct or replace 

 

Engine Control Module faulty 

Replace 

 

Intake Air Temperature Sensor or 
Intake Air Temperature Sensor 
circuit defective 

Correct or replace 

 

Throttle Position Sensor or 
Throttle Position Sensor circuit 
defective 

Correct or replace 

 

Knock Sensor or Knock Sensor 
circuits defective 

Correct or replace 

 

Knock Sensor Module or Knock 
Sensor Module circuits defective 

Correct or replace 

 

6-6 ENGINE DIAGNOSIS (C24SE) 

Hesitation 

Condition Possible 

cause Correction 

Hesitation on acceleration 

Throttle Position Sensor 
adjustment incorrect 

Replace throttle valve assembly 

 

Throttle Position Sensor circuit 
open or shorted 

Correct or replace 

 

Excessive play in accelerator 
linkage 

Adjust or replace 

 

Manifold Absolute Pressure 
(MAP) Sensor circuit open or 
shorted 

Correct or replace 

 

MAP Sensor defective 

Replace 

 

Intake Air Temperature (IAT) 
Sensor circuit open or shorted 

Correct or replace 

 

Knock Sensor (KS) Circuit open or 
shorted 

Correct or replace 

 KS 

defective 

Replace 

 

KS Module circuits open or 
shorted 

Correct or replace 

 

KS Module defective 

Replace 

 

IAT Sensor defective 

Replace 

Hesitation at high speeds  
(Fuel pressure too low) 

Fuel tank strainer clogged 

Clean or replace 

 

Fuel pipe clogged 

Clean or replace 

 

Fuel filter clogged 

Replace 

 

Defective fuel pump system 

Check and replace 

 

Fuel Pressure Control Valve 
leaking 

Replace 

Hesitation at high speeds  
(Fuel injector not working 
normally) 

Power supply or ground circuit for 
Multiport Fuel Injection System 
shorted or open 

Check and correct or replace 

 

Cable of Multiport Fuel Injection 
System disconnected or defective 

Correct or replace 

Hesitation at high speeds 

Engine Control Module defective 

Replace 

 

Throttle Position Sensor circuit 
open or shorted 

Correct or replace 

 

Throttle Position Sensor defective 

Replace 

 

Engine Coolant Temperature 
Sensor circuit open or shorted 

Correct or replace 

 

Engine Coolant Temperature 
Sensor defective 

Replace 

 

MAP Sensor cable open or 
shorted 

Correct or replace 

 

MAP Sensor defective 

Replace 

 

IAT Sensor circuit open or shorted 

Correct or replace 

 

IAT Sensor defective 

Replace 

 

KS Circuit open or shorted 

Correct or replace 

 KS 

defective 

Replace 

 

KS Module circuit open or shorted 

Correct or replace 

 

KS Module defective 

Replace 

 

Throttle valve not wide opened 

Check and correct or replace 

 

Air Cleaner Filter clogged 

Replace filter element 

 

Power supply voltage too low 

Check and correct or replace 

ENGINE DIAGNOSIS (C24SE) 6-7 

Engine Lacks Power 

Condition Possible 

cause Correction 

Trouble in fuel system 

Fuel Pressure Control Valve not 
working normally 

Replace 

 

Fuel injector clogged 

Clean or replace 

 

Fuel pipe clogged 

Clean 

 

Fuel filter clogged or fouled 

Replace 

 

Fuel pump drive circuit not 
working normally 

Correct or replace 

 

Fuel tank not sufficiently breathing 
due to clogged Evaporative 
Emission Control System circuit 

Clean or replace 

 

Water in fuel system 

Clean 

 

Inferior quality fuel in fuel system 

Use fuel of specified octane rating 

 

Engine Control Module supplied 
poor voltage 

Correct circuit 

 

Throttle Position Sensor cable 
disconnected or broken 

Correct or replace 

 

Throttle Position Sensor defective 

Replace 

 

Manifold Absolute Pressure 
Sensor not working normally 

Replace 

 

Intake Air Temperature sensor not 
working normally 

Replace 

 

Engine Coolant Temperature 
Sensor circuit open or shorted 

Correct or replace 

 

Engine Coolant Temperature 
Sensor defective 

Replace 

 

Engine Control Module defective 

Replace 

Trouble in intake or exhaust 
system 

Air Cleaner Filter clogged 

Replace filter element 

 

Air duct kicked or flattened 

Correct or replace 

Ignition failure 

- 

Refer to Hard Start 
Troubleshooting Guide 

 

Heat range of spark plug 
inadequate 

Install spark plugs of adequate 
heat range 

 

Electronic Ignition System with 
module 

Replace