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Hi all. New member here. I recently purchased an '03 Bonneville in great shape with only 66K. It's been great the first 3 months. Sunday it ran fine. Monday morning it ran rough on startup and I thought maybe a sticky EGR since it was chilly out. Didn't smooth out as it warmed up so I put the reader on it and got a P0306. Since the failure happened suddenly, should I look at the plug, wire, or coil first? Thanks in advance for any help. PS I've owned 4 vehicles with a 3800 and this is the first time I've had this happen.
 

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Hi all. New member here. I recently purchased an '03 Bonneville in great shape with only 66K. It's been great the first 3 months. Sunday it ran fine. Monday morning it ran rough on startup and I thought maybe a sticky EGR since it was chilly out. Didn't smooth out as it warmed up so I put the reader on it and got a P0306. Since the failure happened suddenly, should I look at the plug, wire, or coil first? Thanks in advance for any help. PS I've owned 4 vehicles with a 3800 and this is the first time I've had this happen.
P0306; The PCM has detected more than a 2% variance in RPM between the firing of any cylinder in the firing order. In other words you have a misfire. Check, plugs, wires and coil pack. IMO there is a possibility of a vacuum leak or dirty injector as well
 

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PS, that po306 is a missfire code for cylinder number 6..... Start there.... check plug, wire, the look for corrosion inside both ends of the plug wire boots as well as corrosion on the coil terminals where the wires plug on.

PS, PO 301-302-303-304-305-306 are cylinder numbers...... Jake
 
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