Exhaust Back Pressure Sensor
Install a "T" in vacuum line between EGR valve and Exhaust Back Pressure Sensor and attach a vacuum gauge to "T". Start engine and allow to idle. No vacuum should be indicated. Accelerate engine to 2000 RPM and observe vacuum gauge for following: if coolant temperature is below 115°F, no vacuum should be indicated. If coolant temperature is above 115°F, carburetor ported vacuum should be indicated. If no vacuum was indicated during test, be sure vacuum is being applied to inlet side of sensor. Then remove sensor and inspect spacer port and tube for restrictions. Restrictions caused by carbon or lead deposits can be removed with spiral wire brush. Otherwise, replace Back Pressure Sensor.