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Old 11-19-2017, 01:38 PM   #1
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DTC Codes P0300, P0305, P0306, P0304

My 2001 Boxster is making me nuts. Recent engine work:

- Replaced AOS
- Replaced MAF
- Replaced all four oxygen sensors
- Replaced coolant reservoir and all hoses
- Cleaned throttle body and intake plenum

Car is running rough at idle and showing CEL with DTC Codes P0300, P0305, P0306, P0304 (see attached image).



Any thoughts on what could be causing this?

Thank you!!!
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Old 11-19-2017, 02:25 PM   #2
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300 is a general misfire (most likely caused by the other codes).

The codes are all for cylinders on the same side. Have you replaced spark plugs or disconnected coil packs?

I'd look at the coil connectors and make sure all are connected to the correct cylinders and seated all the way. Sometimes its hard to tell if coil pack connector is completely seated. there should be an audible click.
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Old 11-19-2017, 03:18 PM   #3
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First buy a "Super-Met-Al" paint pen.
Then mark the Bank 1 coil connectors in the correct cylinder sequence. You have no Bank 1 codes right?
Then disconnect the coil connectors on Bank 2 and figure out the correct sequence.
When you get the cylinder sequence right, the engine will run sweetly but may produce clouds of white smoke- caused raw gas from the misfire in the headers/cats. This is potentially dangerous for obvious(I hope) reasons. When the smoke clears (or the flames die down) , Mark the correct cylinder # on (the charred remains of ?) each coil connector
Someone over on Renntech recently did a long Post on this issue and gave all the fumbling errors and diagnostics.
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Old 11-19-2017, 03:24 PM   #4
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I've not changed the plugs or messed with the coils. I did have a shop replace the coolant reservoir and lines so perhaps they messed this up as it was running smoothly before I took it in.
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Old 11-19-2017, 03:30 PM   #5
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O.K. vacuum leak on Bank 1
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Old 11-19-2017, 06:41 PM   #6
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Quote:
Originally Posted by Gelbster View Post
O.K. vacuum leak on Bank 1
+1 As you have not messed with spark plugs.
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