Use a hose as big as you can go but small enough to fit the hole and either duct, masking, or whatever tape the hose to the shop vac.
Until you said you had 40 psi in cylinder 3 I was thinking we might have the same problem! My ‘99 had p0303 and just a slight misfire sound at idle but seem to run good and rev well in neutral, felt good under load and otherwise. But cylinder 3 for me was 145 or so and other cylinders 160-165. I’m starting to think my problem is something malfunctioned on just that cyl/piston before I got it or debris got sucked through cylinder 3 at some point.
Until you said you had 40 psi in cylinder 3 I was thinking we might have the same problem! My ‘99 had p0303 and just a slight misfire sound at idle but seem to run good and rev well in neutral, felt good under load and otherwise. But cylinder 3 for me was 145 or so and other cylinders 160-165. I’m starting to think my problem is something malfunctioned on just that cyl/piston before I got it or debris got sucked through cylinder 3 at some point.