P0306 and running rough at idle - 3800Pro.com Forum
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Go Back   3800Pro.com Forum > Engine > DTC's, Problems & Troubleshooting

DTC's, Problems & Troubleshooting Getting an engine related DTC? Check here for assistance.

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Old 08-21-2011, 02:28 PM
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P0306 and running rough at idle

I'm getting a P0306 trouble code. The car is running rough at idle, seems to run a little better when you increase the throttle, but still seems like it might be missing. I checked the coil, swapped it out with another coil, both tested okay. Checked the wires which were replaced about 6 months ago, replaced all 6 plugs, checked the injector resistance and all were okay, pulled the injectors and cleaned them and still have the same issue. I replaced the upper intake manifold at 58,000 miles when it ruptured and dumped coolant into the engine. Also replaced the lower intake manifold gaskets. At that time I had replaced the plugs. The car has 67,000 miles on it now and whe I just pulled the plugs they smelt like old gas, yet the car is driven daily about 50 miles. Any ideas where my problem is?
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Old 08-27-2011, 04:31 PM
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Bump for help!

Replaced the MAP Sensor today. All the plug wires checked out with an inline spark tester. Still running rough at idle. Long term Fuel Trim is at 16+%, Short Term Fuel Trim is at 10+%. Pulled the plug on the MAF and the Long Term Fuel Trim droped to -2% then jumped to 21+%. Vacuum leak? Compression issue? I need help!
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Old 09-03-2011, 06:37 PM
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Freeze Frame data from the P0300 code that showed up today.

P0300 is the DTC that caused this Freeze Frame Data to be Stored Random/Multiple Cylinder Misfire Detected

Fuel System 1 Status Closed Loop Control using Oxygen Sensor - Normal
Calculated Load 6.3 %
Coolant Temperature 93 Deg C 199.4 Deg F
Short Term Fuel Trim Bank 1 0.78 % Rich (+)
Long Term Fuel Trim Bank 1 0.00 %
Intake Manifold Pressure 76 kPaA 11.0 PsiA
Engine Speed 1533.75 Rpm
Vehicle Speed 55 Kmh 34 Mph
Mass Air Flow 11.32 g/s 1.5 lb/min
Absolute Throttle Position 3.1 %

Any ideas?

Battery has been replaced, fuel filter replaced. MAF sensor cleaned. Checked the alternator and it seems to be okay, putting out about 12 v at idle, no shorts.
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Old 09-19-2011, 04:16 PM
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Did you ever find the issue?

I'm having the same problem, but I have only got P0306 to show up. (Misfire in cylinder 6)

Replaced Plugs, wires, and coil pack..
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Old 09-19-2011, 09:39 PM
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I didn't get time to play with it this past weekend. I haven't gotten any responses here, so I've checked with a few mechanics and have been told it could be a sticking EGR valve, a vacuum line leak or a vacuum leak at the intake manifold, so that's what I'm going to check next. I'll keep you posted as to what I find out.
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