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make sure you have no vacuum leaks.the problem may be a bad ignition module i will give you a chart to help you find this problem
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DTC P0300 Engine Misfire Detected Circuit Description The crankshaft position (CKP) sensor is the primary input to determine if misfire is occurring. Engine misfire is detected by monitoring crankshaft speed variations between cylinders. If a crankshaft deceleration occurs during a combustion or power stroke, the control module will compare this change in crankshaft speed to the previous cylinder. If the crankshaft speed change is more than a maximum allowable speed, the misfire is detected. Misfire may occur in a specific cylinder or in all cylinders randomly.When an engine is misfiring, brief decelerations in crankshaft rotational speed will be detected by the CKP. The control module determines which cylinder has misfired based upon the camshaft position (CMP) sensor input. Misfire data is stored for each cylinder in separate accumulators. After 100 combustion events, the misfire totals are compared to a calibrated maximum number. If the misfire is excessive, this diagnostic trouble code (DTC) will set.Conditions for Running the DTC
Conditions for Setting the DTC The VCM detects a deceleration in the crankshaft speed characteristic of either an emission type misfire or a catalyst damaging type misfire.Action Taken When the DTC Sets If the VCM determines that the engine misfire is significant enough to have a negative impact on emissions, the VCM turns ON the malfunction indicator lamp (MIL) after the misfire has been detected on 2 non-consecutive trips under the same operating conditions. If the misfire is severe enough that catalytic converter damage could result, the MIL flashes while the misfire is present.Conditions for Clearing the MIL or DTC
Diagnostic Aids The Misfire Index counts the number of misfires. The scan tool can monitor the Misfire Index. There is a current and history misfire counter for each cylinder. Use the current misfire counter in order to determine which cylinder is misfiring or use the history misfire counter for misfires that are not currently present.Many different conditions could cause an intermittent misfire.Check for the following conditions:
Sticking intake or exhaust valves on engines with a misfire when cold.Check HO2S for abnormal voltage readings.Check for a vacuum leak as a possible cause of the engine misfire.An intermittent may be caused by any of the following conditions:
Thoroughly check any circuitry that is suspected of causing the intermittent complaint.Test Description The numbers below refer to the step numbers on the diagnostic table.