Consistent P0306 when cold - RESOLVED
1996 Bonneville SE 3.8 VIN K
The issue turned out to be a broken valve spring on #6 intake. A $5 fix. It'* the first time I've ever experienced an intermittent fault for this problem.
I get a consistent P0306 cylinder 6 misfire until the engine warms up. At warmup the misfire goes away and the MIL stops blinking. I've checked or done the following:
- switched around plugs
- switched around coils
- switched around ignition wires (no contact with O2 sensor in the rear)
- UIM is new, LIM gaskets new (updated aluminum type)
- switched around fuel injectors
- checked for vacuum leaks and replaced worn hoses
I use Autotap and the issue always involves #6, along with a generic P0300 code. I'd suspect a head gasket but a forum search suggests that this is really rare. The O2 sensor shouldn't be involved because the engine is in closed loop when the problem occurs. Any suggestions/advice appreciated.