1993 Volvo 940 Emissions testing and EGR system

My car was due for its smog check (California-Enhanced Area-Star Test Only Required), It passed the visual inspection and functional check but failed the emissions test Gross Polluter limits for HC, CO, & NO. Based on this, I decided to have a mechanic look at the test results and check out the car and it's mechanical history. I told him the car uses quite a bit of oil (Mobil1 Full Synthetic) at the rate of about 1qt per week but it doesn't smoke and generally runs pretty good with ok gas mileage (15-20mpg). The mechanic did a compression test and 3 cylinders tested at 110psi and 1 at 120psi. Based on this he suggested that the valve stem seals should be replaced and installed the new seals without removing the head. He also inspected and repaired or cleaned all the vacuum lines and other emissions system components including the EGR system components and changed the oil and filter. The distributor cap, rotor, plug wires, plugs, air filter, and fuel filter had all been replaced recently and the catalytic converter about 2 years ago. After all the work was done including setting the timing, I drove the car and it seemed to run ok but the check engine light came on. I ran the OBD tests and received a code of 2-4-1 (EGR system flow too low, cause: EGR vacuum booster). I reset the OBD and drove the car aggressively for about 30 minutes, it seemed to run ok and the check engine light did not come back on so I took the car the get the smog retested. This time it passed the visual inspection and functional checks but again failed the emissions test but this time only the NO. The results of the emissions tests were as follows:

Test #1 (before all the work was done)
M1-15mph, rpm-1776, %CO2-12.5, %O2-1.2,
HC(ppm)-Max 59 Meas 141, CO(%)-Max 0.50 Meas 2.31, NO(ppm)-Max 549 Meas 563
M2-25mph, rpm-1783, %CO2-13.2, %O2-1.2,
HC(ppm)-Max 35 Meas 48, CO(%)-Max 0.47 Meas 1.23, NO(ppm)-Max 502 Meas 286

Re-Test #1 (after all the work was done)
M1-15mph, rpm 1728, %CO2-14.8, %O2-0.3,
HC(ppm)-Max 59 Meas 26, CO(%)-Max 0.50 Meas 0.04, NO(ppm)-Max 549 Meas 945
M2-25mph, rpm-2100, %CO2-14.8, %O2-0.2,
HC(ppm)-Max 35 Meas 17, CO(%)-Max 0.47 Meas 0.01, NO(ppm)-Max 502 Meas 945

As you can see, passed HC and CO but failed NO.

At this point in time, my mechanic is only available in the evening but I have to get the car to pass smog by Wednesday 11/19/2014 (tomorrow) so I need to continue troubleshooting until my mechanic is available.

My first thought is the OBD code of 2-4-1 EGR system flow too low, cause: EGR vacuum booster. Can you tell or show me where this component is located and what is the procedure for testing it?