1989 Toyota Camry engine surging

My Camry has a manual tranny, 4 cyl, 200K+ miles. Just recently the 'check engine' light has flashed at me three times, once a day. The symptom happens when it's at operating temperature. The rpms go up hold for a few seconds then go down to normal. Other than that it runs fine.
Am I correct to think this is a sensor problem or a connection to the sensor problem? How is the best way to make sure that the repair place tracks down the correct sensor and gets it fixed the first time.

Thanks