I have had this problem for a while now and still havnt resolved it. My camaro, a 99 v6, is misfiring when it has been sitting for about a day and when the tempererature outside is really cold. I Dont have an IAC valve and it isnt my air temperature sensor. The only code that I am being sent is p0300. After it has been running for 3 minutes or so, it calms down and runs just fine. I dont hear any vaccume leaks, but I really dont think this would be it because it does run just find after a few minutes. Any more Ideas?

 

P 0300 is random multiple misfires. Usually due to ignition problems or lean fuel mixture. There may be a marginal ignition control module that does not like the cold, low fuel pressure at start up, a bad ECT sensor not reporting the proper temp (this won't set codes, but the temp reported can be seen on a scanner), and causing the PCM to order a lean condition.
What happened to the Idle Control Valve?

If you are sure the misfire is random, check for the following conditions:[*]System grounds-Ensure that all connections are clean and properly tightened.[*]The mass air flow (MAF) sensor-A 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 air flow sensor.[*]A 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.[*]The 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, for an incorrectly installed or malfunctioning crankcase ventilation valve, or for vacuum leaks at the throttle body, the EGR valve, and the intake manifold mounting surfaces.[*]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.[*]Fuel injectors-Perform Fuel Injector Coil Test.[*]Water contamination in the fuel system can cause a single cylinder to misfire as well as cause a random misfire.[*]The exhaust gas recirculation (EGR) system-Check for a 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 (HO2S). 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 OTC 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 .
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