Missing. I get a code p0300 on the DTC. I changed out the air mass flow with and tried it on another vehicle. Changed out the coil packs one by one on a 2004 chevy tahoe 5.3 liter. changed out the plug wires first. so here I am wondering if anyone has a suggestion.

Multiple misfires can be caused by a few different things , intake manifold vacuum leaks , low fuel pressure , basic things like plug wires an spark plugs needing to be changed if hasn't been done already . How many miles on the vehicle ? If over 100,000 K timing chain an gear wear can also cause this . The powertrain control module (PCM) uses information from the ignition control (IC) module and the camshaft position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring the variations in the crankshaft rotation speed for each cylinder the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause the three-way catalytic converter to overheat under certain conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for 3-way catalytic converter overheating are present.
If the misfire is random, check for the following conditions:
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System grounds

Ensure all connections are clean and properly tightened.

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Mass air flow sensor

A mass air flow (MAF) sensor output that causes the PCM to sense a lower than normal air flow will cause a lean condition. Try operating the vehicle within the Failure Records conditions with the MAF sensor disconnected. If the lean or misfiring condition is not present with the MAF sensor disconnected, replace the Mass Airflow Sensor Replacement .

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Damaged accessory drive belt or driven accessory

A damaged serpentine belt or belt driven accessory can cause engine load variations sufficient to set a misfire DTC.

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Air induction system

Vacuum leaks that cause intake air to bypass the MAF sensor will cause a lean condition. Check for disconnected or damaged vacuum hoses, incorrectly installed or malfunctioning crankcase ventilation valve, or for vacuum leaks at the throttle body, exhaust gas recirculation (EGR) valve, and intake manifold mounting surfaces.

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Fuel pressure

Perform a fuel system pressure test. A malfunctioning fuel pump, a plugged filter, or a malfunctioning fuel system pressure regulator will contribute to a lean condition. Refer to Fuel System Diagnosis .

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Fuel injectors

Refer to Fuel Injector Solenoid Coil Test .

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Water contamination in the fuel system can cause a single cylinder to misfire as well as cause a random misfire, refer to Alcohol/Contaminants-in-Fuel Diagnosis .

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EGR system

Check for leaking valve, adapter, or feed pipes which will contribute to a lean condition or excessive EGR flow.

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Extended idle

Excessive Open Loop operation caused by extended idling or short trip driving may leave deposits on the heated oxygen sensors. The deposits cause oxygen sensors to respond slowly to exhaust oxygen content, affecting fuel control and causing a misfire to be indicated at idle. This condition is not permanent. To determine if this condition is causing the DTC P0300 to set, review the Freeze Frame/Failure Records for DTC P0300. If the DTC P0300 occurs at high engine speeds, the condition described above did not cause the DTC to set. If the DTC P0300 occurs at idle or very low engine speeds and at engine coolant temperatures below 80?°C (176?°F), the condition described above is very likely the cause of the DTC to set. The deposits on the heated oxygen sensors can be eliminated by operating the vehicle fully warm at mass air flows above 15 g/s.

Coil pack may be bad

P0300 is a random misfire means different cylinders are missing at random. so you have a problem that's common to one thing.

A VACUUM LEAK!

P0300 Diagnostic Code - Random Misfire Technical Description Random/Multiple Cylinder Misfire Detected What does that mean? Basically this means that the the car's computer has detected that not all of the engine's cylinders are firing properly. A P0300 diagnostic code indicates a random or multiple misfire. If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring. A P0302 code, for example, would tell you cylinder number two is misfiring. Unfortunately, a P0300 doesn't tell you specifically which cylinder(s) is/are mis-firing, nor why. Symptoms Symptoms may include: the engine may be harder to start the engine may stumble / stumble, and/or hesitate other symptoms may also be present Causes A code P0300 may mean that one or more of the following has happened: Faulty spark plugs or wires Faulty coil (pack) Faulty oxygen sensor(s) Faulty fuel injector(s) Burned exhaust valve Faulty catalytic converter(s) Stuck/blocked/leaking EGR valve / passages Faulty camshaft position sensor Defective computer Possible Solutions If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back. If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors. Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open. It is helpful to have access to a factory service manual and an advanced scan tool to properly diagnose a random misfire DTC. P0300 Diagnostics Video Here is a helpful video that may assist you in learning more, diagnosing, and repairing your P0300 DTC. This video is intended for auto repair professionals but could be helpful to DIYers. It shows use of an advanced OBD-II scan tool during diagnostic steps:

Read more at: http://www.obd-codes.com/p0300
Copyright © OBD-Codes.com Autolite Challenge Series P0300 Engine Misfire Diagnosis

Ive got the same issue with my 2007 Murano. I changed the plugs,ignition coils etc. But try replacing ur MAF (Mass Air Flow Sensor). Hope that helps fix ur problem.

If half the engine isn't firing, it may need a new coil pack. Most v6 and v8 engines have a coil pack for each side of the engine. Try swapping them around to see if the other side works; then you'll know. If it's not a coil pack, it's because your car has variable cylinder management, and it has electronics issue.

Hi there:
DTC P1200 - lnjector control circuit


The PCM has the ability to detect a misfire by monitoring the 3X reference and camshaft position input signals from the Ignition Control Module. The PCM monitors crankshaft speed variations (reference period differences) to determine if a misfire is occurring. If 2 percent or more of all cylinder firing events are misfires, emission levels may exceed mandated standards. The PCM determines misfire level based on the number of misfire events monitored during a 200 engine revolution test sample. The PCM continuously tracks 16 consecutive 200 revolution test samples. If 11 or more misfires are detected during any 5 of the 16 samples, DTC P0300 will set. If the misfire is large enough to cause possible three-way catalytic converter damage, DTC P0300 may set during the first 200 revolution sample in which the misfire was detected. In the case of a catalyst damaging misfire, the Malfunction Indicator Lamp (MIL) will flash to alert the vehicle operator of the potential of catalyst damage.


CONDITIONS FOR SETTING THE DTC

* No Vehicle Speed Sensor (VSS), Transaxle, Throttle Position (TP) sensor, Fuel trim, Fuel injector circuit, Engine Coolant Temperature (ECT) sensor, Crankshaft Position (CKP) sensor, Camshaft Position (CMP) sensor, or Mass Air Flow (MAF) sensor DTC(s) set.

* Engine speed between 450 and 5800 RPM.

* System voltage between 9 and 16 volts.

* The ECT indicates an engine temperature between -7 degrees C (19 degrees F) and 120 degrees C (248 degrees F).

* Throttle angle steady.

* The PCM is detecting a crankshaft RPM variation indicating a misfire sufficient to cause three-way catalytic converter damage or emissions levels to exceed mandated standard.


ACTION TAKEN WHEN THE DTC SETS

* If the misfire level is non-catalyst damaging, the PCM will illuminate the MIL during the second key cycle in which the DTC sets.

* If the misfire is severe enough to cause possible catalyst damage, the PCM will immediately flash the MIL while the misfire remains at catalyst damaging levels.

* The PCM will disable Torque Converter Clutch (TCC) operation.

* The PCM will store conditions which were present when the DTC set as Freeze Frame and Fail Records data.


CONDITIONS FOR CLEARING THE MIL/DTC

* The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been run and passed.

* The history DTC will clear after 40 consecutive warm-up cycles have occurred without a fault.

* The DTC can be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed.

DIAGNOSTIC AIDS

The scan tool provides information that can be useful in identifying the misfiring cylinder. If the DTC P0300 is currently stored as DTC status Failed Since Code Clear, the misfire history counters (Misfire Hist #1 - #6) will still contain a value that represents the level of misfire detected on each cylinder. The scan tool displayed misfire counter values (Misfire Hist. #1 through #6) can be useful in determining whether the misfire affects a single cylinder, a cylinder pair (cylinders that share an ignition coil-1/4, 2/5, 3/6), or is random. If the largest amount of activity is isolated to a cylinder pair, check for the following conditions:

* Secondary Ignition Wires.

Check the secondary wires associated with the affected cylinder pair for disconnected ignition wires or for excessive resistance. The wires should measure under 30,000 ohms (30 K ohms). Replace any wires with excessive resistance.

* Damaged Or Faulty Ignition Coil.

Check for cracks, carbon tracking or other damage. Also check coil secondary resistance. Secondary resistance should be between 5000 ohms and 8000 ohms (5 K ohms and 8 K ohms). Replace any faulty coil(s). Refer to Ignition Control Module.

* Substitute a Known Good Coil.

Switch ignition coils and retest. If the misfire follows the coil, replace the ignition coil.

If the misfire is random, check for the following conditions

* System Grounds.

Ensure all connections are clean and properly tightened. Refer to Ground Distribution in Electrical Diagrams.

* Mass Air Flow sensor.

A Mass Air Flow (MAF) sensor output that causes the PCM to sense a lower than normal air flow will cause a lean condition. Try operating the vehicle within the fail records conditions with the MAF sensor disconnected. If the lean or misfiring condition is not present with the MAF sensor disconnected, replace the MAF sensor. Refer to MAF Sensor.

* Damaged accessory drive belt or driven accessory.

A damaged serpentine belt or belt driven accessory can cause engine load variations sufficient to set a misfire DTC.

* Vacuum Leaks.

Vacuum leaks that cause intake air to bypass the MAF sensor will cause a lean condition. Check for the following conditions:

- Disconnected or damaged vacuum hoses. Refer to Emission Hose Routing Diagram.

- Incorrectly installed or faulty crankcase ventilation valve. Refer to Positive Crankcase Ventilation Valve

- Vacuum leaks at the throttle body, EGR valve, and intake manifold mounting surfaces.

* Fuel Pressure.

Perform a fuel system pressure test. A faulty fuel pump, plugged filter, or faulty fuel system pressure regulator will contribute to a lean condition. Refer to Fuel System Pressure Test. See: Computers and Control Systems > Component Tests and General Diagnostics > Fuel System Pressure Test

* Fuel injector(s). Go to Fuel Injector Coil Test. See: Computers and Control Systems > Component Tests and General Diagnostics > Fuel Injector Coil Test

* Contaminated Fuel. Go to Alcohol/Contaminants-in-Fuel Testing Procedure. See: Fuel Delivery and Air Induction > Testing and Inspection

* EGR System.

Check for leaking valve, adapter, or feed pipes which will contribute to a lean condition or excessive EGR flow.

* Extended Idle.

Excessive open loop operation caused by extended idling or short trip driving may leave deposits on the heated oxygen sensors. The deposits cause oxygen sensors to respond slowly to exhaust oxygen content, affecting fuel control and causing a misfire to be indicated at idle. This condition is not permanent. To determine if this condition is causing the DTC P0300 to be set, review the freeze frame and fail records data for DTC P0300. If the DTC P0300 occurs at high engine speeds, the condition described above did not cause the DTC P0300 to set. If the DTC P0300 occurs at idle or very low engine speeds and at engine coolant temperatures below 80 degrees C (176 degrees F), the condition described above is very likely the cause of the DTC P0300 being set. The deposits on the heated oxygen sensors can be eliminated by operating the vehicle fully warm at mass air flows above 15 gm/s.

Important: If the level of misfire was sufficient to cause possible catalyst damage (if the MIL was flashing), ensure that the DTC P0420 test is completed and passed after verifying the misfire repair.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.



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Yes valve cover gasket needs to be replaced, normally for sluggish I would be looking at a MAF mass air flow sensor.

Most likely you do not have bad O2 sensor or coil sience you have P0300 code.
Check for vacuum leaks first , this is very common problem(vacuum leak) , lean mixture will cause misfire. I'm tallking about V6 engine , 4cyl have same problems but for misfire it may have bad coil (they under recall now).
Also check condition of air mass sensor , if it's dirty ,
buy air flow sensor cleaner and clean it according to user manual on the can.(air mass sensor can cause
O2 sensor code)
Check vacuum hose to fuel pressure regulator.
There are many more things to check , but that for mechanic shops after you try this.

try changing the coil packs