The vehicle blows blue/white smoke and misfires on cold startup, with the issue clearing after a few minutes of running.

When started from cold, the engine runs smoothly for a few seconds before beginning to puff blue/white smoke and misfire slightly. The problem disappears once the engine warms up. Disconnecting the EGR valve immediately stops the misfire and smoke, but causes an engine warning light to appear. Multiple workshops had previously inspected and performed extensive work without resolving the issue.