Here is also the details about all the operating modes for the PCM as described above
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IGNITION SWITCH (KEY-ON) MODE
This is an Open Loop mode. When the fuel system is activated by the ignition switch, the following
actions occur:
² The PCM pre-positions the idle air control (IAC) motor.
² The PCM determines atmospheric air pressure from the MAP sensor input to determine basic fuel
strategy.
² The PCM monitors the engine coolant temperature sensor input. The PCM modifies fuel strategy
based on this input.
² Intake manifold air temperature sensor input is monitored.
² Throttle position sensor (TPS) is monitored.
² The auto shutdown (ASD) relay is energized by the PCM for approximately three seconds.
² The fuel pump is energized through the fuel pump relay by the PCM. The fuel pump will operate for approximately three seconds unless the engine is operating or the starter motor is engaged.
² The O2S sensor heater element is energized via the ASD or O2S heater relay. The O2S sensor input is not used by the PCM to calibrate air-fuel ratio during this mode of operation.
ENGINE START-UP MODE
This is an Open Loop mode. The following actions occur when the starter motor is engaged.
The PCM receives inputs from:
² Battery voltage
² Engine coolant temperature sensor
² Crankshaft position sensor
² Intake manifold air temperature sensor
² Manifold absolute pressure (MAP) sensor
² Throttle position sensor (TPS)
² Camshaft position sensor signal
The PCM monitors the crankshaft position sensor. If the PCM does not receive a crankshaft position
sensor signal within 3 seconds of cranking the engine, it will shut down the fuel injection system.
The fuel pump is activated by the PCM through the fuel pump relay. Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off. The PCM determines the proper ignition timing according to input received from the crankshaft position sensor.
ENGINE WARM-UP MODE
This is an Open Loop mode. During engine warmup, the PCM receives inputs from:
² Battery voltage
² Crankshaft position sensor
² Engine coolant temperature sensor
² Intake manifold air temperature sensor
² Manifold absolute pressure (MAP) sensor
² Throttle position sensor (TPS)
² Camshaft position sensor signal
² Park/neutral switch (gear indicator signal—auto. trans. only)
² Air conditioning select signal (if equipped)
² Air conditioning request signal (if equipped)
Based on these inputs the following occurs:
² Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control
the injection sequence and injector pulse width by turning the ground circuit to each individual injector
on and off.
² The PCM adjusts engine idle speed through the idle air control (IAC) motor and adjusts ignition timing.
² The PCM operates the A/C compressor clutch through the A/C compressor clutch relay. This is done
if A/C has been selected by the vehicle operator and specified pressures are met at the high and low–pressure A/C switches. Refer to Heating and Air Conditioning for additional information.
² When engine has reached operating temperature, the PCM will begin monitoring O2S sensor
input. The system will then leave the warm-up mode and go into closed loop operation.
IDLE MODE
When the engine is at operating temperature, this is a Closed Loop mode. At idle speed, the PCM
receives inputs from:
² Air conditioning select signal (if equipped)
² Air conditioning request signal (if equipped)
² Battery voltage
² Crankshaft position sensor
² Engine coolant temperature sensor
² Intake manifold air temperature sensor
² Manifold absolute pressure (MAP) sensor
² Throttle position sensor (TPS)
² Camshaft position sensor signal
² Battery voltage
² Park/neutral switch (gear indicator signal—auto. trans. only)
² Oxygen sensors
Based on these inputs, the following occurs:
² Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control
injection sequence and injector pulse width by turning the ground circuit to each individual injector on
and off.
² The PCM monitors the O2S sensor input and adjusts air-fuel ratio by varying injector pulse width.
It also adjusts engine idle speed through the idle air control (IAC) motor.
² The PCM adjusts ignition timing by increasing and decreasing spark advance.
² The PCM operates the A/C compressor clutch through the A/C compressor clutch relay. This is done if A/C has been selected by the vehicle operator and specified pressures are met at the high and low–pressure A/C switches. Refer to Heating and Air Conditioning for additional information.
CRUISE MODE
When the engine is at operating temperature, this is a Closed Loop mode. At cruising speed, the PCM
receives inputs from:
² Air conditioning select signal (if equipped)
² Air conditioning request signal (if equipped)
² Battery voltage
² Engine coolant temperature sensor
² Crankshaft position sensor
² Intake manifold air temperature sensor
² Manifold absolute pressure (MAP) sensor
² Throttle position sensor (TPS)
² Camshaft position sensor signal
² Park/neutral switch (gear indicator signal—auto. trans. only)
² Oxygen (O2S) sensors
Based on these inputs, the following occurs:
² Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then adjust the injector pulse width by turning the ground circuit to each individual injector on and off.
² The PCM monitors the O2S sensor input and adjusts air-fuel ratio. It also adjusts engine idle
speed through the idle air control (IAC) motor.
² The PCM adjusts ignition timing by turning the ground path to the coil(s) on and off.
² The PCM operates the A/C compressor clutch through the clutch relay. This happens if A/C has been selected by the vehicle operator and requested by the A/C thermostat.
ACCELERATION MODE
This is an Open Loop mode. The PCM recognizes an abrupt increase in throttle position or MAP pressure as a demand for increased engine output and vehicle acceleration. The PCM increases injector pulse width in response to increased throttle opening.
DECELERATION MODE
When the engine is at operating temperature, this is an Open Loop mode. During hard deceleration, the PCM receives the following inputs :
² Air conditioning select signal (if equipped)
² Air conditioning request signal (if equipped)
² Battery voltage
² Engine coolant temperature sensor
² Crankshaft position sensor
² Intake manifold air temperature sensor
² Manifold absolute pressure (MAP) sensor
² Throttle position sensor (TPS)
² Camshaft position sensor signal
² Park/neutral switch (gear indicator signal—auto. trans. only)
² Vehicle speed
If the vehicle is under hard deceleration with the proper rpm and closed throttle conditions, the PCM
will ignore the oxygen sensor input signal. The PCM will enter a fuel cut-off strategy in which it will not
supply a ground to the injectors. If a hard deceleration does not exist, the PCM will determine the proper injector pulse width and continue injection.
Based on the above inputs, the PCM will adjust engine idle speed through the idle air control (IAC) motor. The PCM adjusts ignition timing by turning the ground path to the coil on and off.
WIDE OPEN THROTTLE MODE
This is an Open Loop mode. During wide open throttle operation, the PCM receives the following
inputs:
² Battery voltage
² Crankshaft position sensor
² Engine coolant temperature sensor
² Intake manifold air temperature sensor
² Manifold absolute pressure (MAP) sensor
² Throttle position sensor (TPS)
² Camshaft position sensor signal
During wide open throttle conditions, the following occurs:
² Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off. The PCM ignores the oxygen sensor input signal and provides a predetermined amount of additional fuel. This is done by adjusting injector pulse width.
² The PCM adjusts ignition timing by turning the ground path to the coil(s) on and off.
IGNITION SWITCH OFF MODE
When ignition switch is turned to OFF position, the PCM stops operating the injectors, ignition coil, ASD relay and fuel pump relay.
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So basically monitoring these sensors with an OBDII compliant device would potentially allow you to understand where the issue is and why the engine is behaving in this manner.
There are very cheap OBDII USB wired and Bluetooth adapaters available that can be hooked up to your laptop or smartphone and come with apps that will allow you to read the values returned by these sensors in order to troubleshoot. IMHO these adapters are way better than any OBDII code readers as they can do a lot more for often times a lot cheaper. (But again this my personal opinion)
Hope this will help you resolve your bucking problem.