Intermittent poor acceleration, loss of power. Has

It sounds like there are multiple issues with your Isuzu KB 240 LE. A powerless engine and stalling can be caused by a number of issues, including:

1. Fuel Delivery: If the fuel pump is not delivering enough fuel to the engine, it can cause a loss of power and stalling.
2. Ignition System: If the spark plugs or ignition coils are not functioning properly, it can cause a loss of power and stalling.
3. Mass Air Flow Sensor: A faulty mass air flow sensor can cause the engine to run lean, resulting in a loss of power and stalling.
4. Vacuum Leaks: A vacuum leak can cause a loss of power and stalling.
5. Throttle Body: A dirty or clogged throttle body can cause a loss of power and stalling.
6. Engine Control Module: A malfunctioning engine control module can cause the engine to lose power and stall.
7. Fuel Injection System: A clogged fuel injector or a failing fuel pressure regulator can cause the engine to lose power and stall.

It's recommended to have the vehicle professionally diagnosed to determine the root cause of the problem. The diagnostic process may involve checking the fuel and ignition systems, performing a vacuum leak test, checking the throttle body, and possibly scanning the engine control module for codes. Once the issue is identified, the necessary repairs can be made to restore proper engine performance.

At this point it could be several things, and you'd have to do some testing to start eliminating different possibilities. Could be ignition related-coil, plugs, plug wires, ignition control module, crank sensor, cam sensor, and the associated wiring; could be gas related or the air/fuel mixture is wrong. Or more serious, it could be a mechanical problem like poor compression in one or more cylinders.
I would start with checking the fuel pressure. Borrow or rent a fuel pressure gauge and do a thorough test. Then you will know that the pump and gas delivery to the injectors is not a problem. Next you should check for any possible trouble codes in the pcm. Post back if you need the procedure to get the codes. I can provide a link.

It is nearly impossible to field test for an intermittent miss as far as the ignition system goes. Most people start with new spark plugs and new plug wires to see if that eliminates a miss. The ICM and the ignition coils can be tested at almost any parts store, usually a free service.
Maybe this will help a little, give you an idea of things to check or consider. Engine misses are caused by lack of, or wrong amount of 1) gas, 2)spark, or 3) cylinder compression.

The crankshaft position sensor identifies position of the crankshaft to the ignition control module (ICM), engine control module (ECM) or powertrain control module (PCM)

When not replaced, vehicle could experience no- or hard start, long crank time, misfire, lack of power, excessive hydrocarbons in oil, spark plug fouling, catalytic converter failure, poor fuel economy, CEL/MIL illumination or intermittent shutdown.

The camshaft position sensor identifies position of the camshaft to the ignition control module (ICM), engine control module (ECM) or powertrain control module (PCM)

When not replaced, vehicle could experience no- or hard start, long crank time, misfire, lack of power, excessive hydrocarbons in oil, spark plug fouling, catalytic converter failure, poor fuel economy, CEL/MIL illumination or intermittent shutdown

Cauases or fault codes are not cut and dry, but here are the possible causes of codes P0316 and P0306 which are related codes.
P0316 - Engine Misfire Detected on Startup
Symptoms - Engine Light ON (or Service Engine Soon Warning Light)
- Engine fails to start
- Engine runs rough Possible causes - Crankshaft Position (CKP) sensor harness is open or shorted
- Crankshaft Position (CKP) sensor circuit poor electrical connection
- Faulty Crankshaft Position (CKP)
- Ignition System
- Fuel Injectors
- Running out of fuel
- Fuel Quality
- Faulty Engine Control Module (ECM) P0306 - Cylinder 6 Misfire Detected Symptoms - Engine Light ON (or Service Engine Soon Warning Light)
- Lack/loss of power
- Hard start
- Engine hesitation
Possible causes - Faulty spark plug 6
- Faulty ignition coil 6
- Ignition coil 6 harness is open or shorted
- Ignition coil 6 poor electrical connection
- Clogged or faulty fuel injector 6
- Injector 6 harness is open or shorted
- Injector 6 poor electrical connection
- Improper spark plug 6
- Insufficient cylinder 6 compression
- Incorrect fuel pressure
- Intake air leak

You can't just change the crankshaft postion sensor an expect it to work correctly > Has to have
Crankshaft Position System Variation Learn done !
you need a factory scan tool Tech 2
Install a scan tool.
Monitor the powertrain control module for DTCs with a scan tool. If other DTCs are set, except DTC P0315, refer to Diagnostic Trouble Code (DTC) List for the applicable DTC.
Select the crankshaft position variation learn procedure with a scan tool.
The scan tool instructs you to perform the following:
4.1. Accelerate to wide open throttle (WOT).
4.2. Release throttle when fuel cut-off occurs.
4.3. Observe fuel cut-off specification for applicable engine.
4.4. Engine should not accelerate beyond calibrated RPM value.
4.5. Release throttle immediately if value is exceeded.
4.6. Block drive wheels.
4.7. Set parking brake.
4.8. DO NOT apply brake pedal.
4.9. Cycle ignition from OFF to ON.
4.10. Apply and hold brake pedal.
4.11. Start and idle engine.
4.12. Turn A/C OFF.
4.13. Vehicle must remain in Park or Neutral.
4.14. The scan tool monitors certain component signals to determine if all the conditions are met to continue with the procedure. The scan tool only displays the condition that inhibits the procedure. The scan tool monitors the following components:
• Crankshaft position (CKP) sensors activity--If there is a CKP sensor condition, refer to the applicable DTC.
• Camshaft position (CMP) signal activity--If there is a CMP signal condition, refer to the applicable DTC.
• Engine coolant temperature (ECT)--If the engine coolant temperature is not warm enough, idle the engine until the engine coolant temperature reaches the correct temperature.
Enable the crankshaft position system variation learn procedure with the scan tool and perform the following:
Important: While the learn procedure is in progress, release the throttle immediately when the engine starts to decelerate. The engine control is returned to the operator and the engine responds to throttle position after the learn procedure is complete.

DTC P0336
No 18X reference pulses are received in one engine cycle, 720 degrees of crankshaft rotation.

Attempt to start the engine.
Does the engine start and run?
--
YES - Go to Step 3
NO - Go to Step 8
3
Observe the 18X Crank Sensor parameter with the scan tool.
Does the 18X Crank Sensor parameter change with engine speed?
--
YES - Go to Step 4
NO - Go to Step 5
4
Observe the Freeze Frame/Failure Records for this DTC.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Does the DTC fail this ignition?
--
YES - Go to Step 5
NO - Go to Testing for Intermittent Conditions and Poor Connections
5
Turn OFF the ignition.
Disconnect the ignition control module (ICM).
Turn ON the ignition, with the engine OFF.
Connect a test lamp to a good ground.
Probe the 18X reference medium resolution engine speed signal circuit at the ICM connector with the test lamp.
Does the test lamp illuminate?
--
YES - Go to Step 10
NO - Go to Step 6

6
Connect the test lamp to battery voltage.
Probe the 18X reference medium resolution engine speed signal circuit at the ICM connector with the test lamp.
Does the test lamp illuminate?
--
Yes - Go to Step 9
No - Go to Step 7
7
Observe the 18X Crank Sensor parameter with the scan tool.
Probe the 18X reference medium resolution engine speed signal circuit repeatedly at the ICM connector with the test lamp.
Does the 18X crank sensor RPM change?
--
Yes - Go to Step 13
NO - Go to Step 11
8
Disconnect the crankshaft position (CKP) sensor.
Turn ON the ignition, with the engine OFF.
Measure the voltage from the CKP sync signal circuit to a good ground with a DMM.
Is the voltage within the specified range?
4-8 V
Go to Step 14
Go to Step 12
9
Test the 18X reference medium resolution engine speed signal circuit between the ICM and the powertrain control module (PCM) for a short to ground. Refer to Wiring Repairs .
Did you find and correct the condition?
--
Go to Step 20
Go to Step 19
10
Test the 18X reference medium resolution engine speed signal circuit between the ICM and the PCM for a short to voltage. Refer to Wiring Repairs .
Did you find and correct the condition?
--
Go to Step 20
Go to Step 19
11
Test the 18X reference medium resolution engine speed signal circuit between the ICM and the PCM for an open. Refer to Wiring Repairs .
Did you find and correct the condition?
--
Go to Step 20
Go to Step 16
12
Test the CKP sync signal circuit for an open. Refer to Wiring Repairs .
Did you find and correct the condition?
--
Go to Step 20
Go to Step 15
13
Inspect for the following conditions:
• Incorrect harness routing near secondary ignition components
• The ignition coil arcing to the wiring harness or to the ICM
• The ignition coils for cracks, carbon tracking, or other signs of damage--Refer to Ignition Coil Replacement .
• Spark plug wires arcing--Refer to Spark Plug Wire Inspection .
Did you find and correct the condition?
--
Go to Step 20
Go to Step 15
14
Test for an intermittent or for poor connections at the CKP sensor. Refer to Testing for Intermittent Conditions and Poor Connections .
Did you find and correct the condition?
--
Go to Step 20
Go to Step 17
15
Test for an intermittent or for poor connections at the ICM. Refer to Testing for Intermittent Conditions and Poor Connections .
Did you find and correct the condition?
--
Go to Step 20
Go to Step 18
16
Test for poor connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections .
Did you find and correct the condition?
--
Go to Step 20
Go to Step 19
17
Replace the CKP sensor. Refer to Crankshaft Position Sensor Replacement .
Did you complete the replacement?
--
Go to Step 20
--
18
Replace the ICM. Refer to Ignition Control Module Replacement .
Did you complete the replacement?
--
Go to Step 20
--
19
Replace the PCM. Refer to Powertrain Control Module Replacement for replacement, setup, and programming.
Did you complete the replacement?
--
Go to Step 20
--
20
Clear the DTCs with a scan tool.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition?
--
Go to Step 2
Go to Step 21
21
Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?
--
Go to Diagnostic Trouble Code (DTC) Types
System OK
P0300 is a random misfire !

Regardless of age, battery discharging first needs to be addressed and fixed - bad battery or something in car (like a light) may be staying on when car is shut off.
Fuel pressure is too low - should be around 50psi and may be caused by an intermittent fuel pump or regulator problem.
The cause of the other problems is usually with the IAC or MAF sensors or the EGR valve - fouling at the EGR, IAC and/or throttle body is to be expected for a car this old.

CHEK THE STARTER RELAY DONT KNOW WHERE THEY PUT IT BUT FIND IT AND CHECK IT

crank shaft position sensor is most likely cause. Do check ignition and fuel pump relays with an ohmmeter to make sure they are not faulty. Check power to ignition module. You can also check crank sensor with the ohmmeter. Check all vacuum hose and also check throttle position sensor.

Probably the ignition timing is not advancing the spark on acceleration or high rpm's.

That is the job of the ECM (Electronic Control Module). Check it / Replace it.

Hope this helps!