All 1973 models are equipped with an exhaust gas recirculation (EGR) system to control oxides of nitrogen. Because the system channels exhaust gases through narrow passages into the induction system, deposits build up quickly in the system, eventually blocking the exhaust gas recirculation flow. Therefore, to keep the car's emission levels up to federal standards, it is necessary to service the system at the recommended intervals. EGR service consists of cleaning or replacing the EGR valve, and cleaning all of the exhaust gas channels.
Remove the EGR valve for cleaning. Do not strike or pry on the valve diaphragm housing or supports, as this may damage the valve operating mechanism and/or change the valve calibration. Check orifice hole in the EGR valve body for deposits. A small hand drill of no more than 0.060 inch diameter may be used to clean the hole if plugged. Extreme care must be taken to avoid enlarging the hole or damaging the surface of the orifice plate.
Remove the carburetor and carburetor spacer on engines so equipped. Clean the supply tube with a small power-driven rotary type wire brush or blast cleaning equipment. Clean the exhaust gas passages in the spacer using a suitable wire brush and/or scraper. The machined holes in the spacer can be cleaned by using a suitable round wire brush. Hard encrusted material should be probed loose first, then brushed out.