You likely have a sticking EGR, which you momentarily "freed" with the screwdriver tapping. As Tone mentions cleaning the EGR and tube of carbon deposits will help, for a while. Excessive deposit build-up is a sign of a sticking or intermittent EGR problem. Unfortunately, this is more indicative of the design and is very common among a wide-range of EGR designs in use on passenger vehicles. More and more new EGR valves are touting "non-stick" designs, so maybe there's one out there that can be retro-fitted to our V6.

It'd be nice if we could each have one of these in the tool chest: EGR Tester But at $250 a pop it's a pricy tool for an occasional problem.

For those interested in what the EGR system is and why you don't necessarily want to bypass it, here's a pretty decent article: Understanding EGR Systems.