I honestly cant help you on testing the modulator-never had to go that far...and with spare parts inventory I have, just swapped things like that out if I thought it didnt work right. Location of this sensor is somewhere on the EGR tube leading to the back of the plenum...follow the wires. Cant find a picture showing location at the moment. But I did find this at autozone.com :

EGR Valve Thermo-Sensor

Disconnect the electrical lead which runs to the EGR valve thermo-sensor.

Remove the thermo-sensor from the side of the EGR valve.

Heat the thermo-sensor in a pan of water to the following temperature: 260?F.

Connect an ohmmeter, in series with a 10ω resistor, between the thermo-sensor terminal and case.

With the ohmmeter set on the kω scale, the following reading should be obtained: 2.55Kω

Replace the thermo-sensor if the ohmmeter readings vary considerably from those specified.

To install the thermo-sensor on the EGR valve, tighten it to 15-21 ft. lbs.


CAUTION

Do not tighten the thermo-sensor with an impact wrench.




Checking the EGR Vacuum Modulator

Tag and disconnect all hoses leading form the vacuum modulator.

Remove the vacuum modulator.

Unscrew the vented top plate and remove the filter.

Check the filter for any contamination or other damage.

Clean the filter using compressed air.

Installation is in the reverse order of removal.


Hope this helps you some. When I say that I hit the EGR valve with a wrench I was dead serious. Now if this knocked some carbon off the plunger or just jolted the connector enough to make a better connection I dont know. Start with the wiring, make sure its not damaged then move on from there. If I find the picture I was looking for I'll pass it along.
~Darin <img src="/forums/images/graemlins/baby.gif" alt="" />