2000 Daewoo Leganza 2.2L Running with PO303 Code and Backfiring Through Intake - Need Help

Model: Daewoo Leganza Fault Code: P0303 Posted: 2012-04-26 16:26

I'm looking for help diagnosing a persistent issue on my 2000 Daewoo Leganza SE with a 2.2L engine. The car runs but consistently backfires through the intake manifold and sets a diagnostic trouble code PO303 (Cylinder 3 Misfire). I've performed several checks: compression tests show all cylinders at 160 psi, indicating no significant valve sticking or mechanical issues. Cam timing has been verified and is correct for both cams. Fuel pressure and leak test results are normal. Spark plugs are blackened, suggesting rich mixture conditions. I have already replaced the spark plugs, plug wires, and coil pack to rule out ignition-related causes — but the problem persists. A leak-down test confirmed no leaks from cylinders or through intake valves. Despite these checks, the PO303 code remains active and backfiring continues. Any additional troubleshooting steps or potential root causes for this specific issue in a 2000 Daewoo Leganza? Thanks for any insights.