It isn't dumb. Engineers put this stuff onto engines to confuse and baffle the week-end mechanic. Oh, for the return of the six cylinder flat head...
In a nutshell: vacuum for the EGR comes from the throttle chamber but, it has to pass two mechanical "yes or no" tests before it gets there. First test; "Is is the engine warm"? That question is from the thermal valve under the intake manifold. If you follow the line from the transducer (toward front of engine) down through the manifold you'll see it terminate on the valve (small cylinder with two ports sticking straight up) the other line attaches to the throttle chamber. When the engine is cold no vacuum can pass through it. This is good because on a cold start you don't want the EGR choking the engine with exhaust gas before it can handle it. It'll just stall. Once the engine is warm that valve opens and allows vacuum to the second test: the back pressure transducer.
The BPT is like a metering device. It's question is "Is the throttle open?". It get's it's answer by measuring the pressure in the exhaust. It's got a diaphram that opens and closes to either let vacuum pass or cut it off. The diaphram is pushed by the pressure in the exhaust (back pressure). It get's that pressure from the same tube that feeds exhaust gas to the throttle chamber and it's fed to the bottom port of the back pressure transducer. It's operation is real simple. At idle the EGR is closed because fuel is at a minimum and exhaust gas would choke the engine. That's why the finger push method on the EGR does what it does. At part throttle the pressure in the exhaust increases so the diaphram in the transducer pushes up and opens the passage for vacuum between the EGR and the throttle chamber. Now you get an increase in fuel so the engine can handle a little exhaust gas.
If you floor it the back pressure goes way up, so the transducer pushes the diaphram even harder and closes off the passage of vacuum to the EGR. The whole purpose of the EGR is to reduce co2 and Nox emissions (the solution to pollution is dilution) by mixing in some heat and recycle some spent gases, but it can't be too much or too little cause the computer expects the mechanical things to do their job the same way every time. If you could convice the computer that it doesn't need the EGR maybe you could take it out, but as long as that line of code is in the instructions it better be working.
Believe me this EGR had me confused until I finally decided to stop thinking about it and just fix it. If you watch it in operation the movement of the EGR is so slight you wonder if it's doing anything at all, but the 2.6 is all about little things causing big problems.
