egr problem

I recently bought a Mazda 626 V6 with a manual transmission and 131000 miles. I test drove the car for about 10 minutes and it seemed to run fine. At that time the engine light was not on. After I pulled out of the parking lot, i decided to really give it some gas on the highway just to see what kinda of pick-up it had. Immediately after doing so, the engine light came on and remains on now. The car seems to idle high in my opinion (about 2300 rpm). All the gauges are reading in the normal range (besides the tachometer), the light is just on. I went and bought a code scanner and pulled the code p1402, which was a code for the egr valve position sensor circuit. Its my educated guess that the high idle and the egr trouble are related. I would greatly appreciate some insight on how to properly diagnose this problem as the egr valve is too expensive to change it on an assumption. Thanks for your time, Mike.