See Figures 1 and 2
The EFE system uses a throttling type valve in the exhaust manifold on one side of V6 and V8 engines. The valve is actuated by a vacuum diaphragm and will quickly develop operating problems if it binds due to corrosion. The shafts should be thoroughly soaked with a solvent designed to remove rust from heat risers every 30,000 miles. There is also an electrically heated EFE system used. For details on the EFE system refer to Driveability & Emissions Controls in this information.
Every 30,000 miles, apply 10 in. of vacuum to the valve from an external source, or start the engine from an overnight cold condition. The valve should close all the way. If the valve binds and cannot be unstuck through application of solvent, it should be replaced.