The exhaust gas recirculation, or EGR, valve in your 1987 Ford Ranger 2.9L engine allows small amounts of exhaust gases into the intake manifold. These gases mix with the air and fuel inside the combustion chambers to lower the temperature and reduce hazardous emissions. Thus, it is common for carbon buildup and miles of service to have their adverse effect on the EGR valve. Still, you can troubleshoot the valve at home to help you diagnose the component's condition before you decide it is time to replace it.
Open the hood and locate the EGR valve and the idle air control valve. You will find the EGR valve around the top area of the engine. Look for a round, flat, metal component, about three to four inches in diameter. It has a small vacuum hose connected on top and a pipe, connected to the bottom of the valve leads to the exhaust manifold.
Make sure the two EGR valve-mounting bolts are tight and the vacuum hose is well connected and undamaged.
Start the engine and allow it to idle for about 20 minutes so that it reaches operating temperature. Disconnect the vacuum hose from the EGR valve and attach a vacuum gauge to the hose. The gauge should read less than 1.0-inch Hg (3.4 kPa) of vacuum. If the gauge registers more vacuum than the specified, inspect the EGR solenoid for proper operation.
Locate the idle air control, or IAC, valve. This valve mounts on the throttle body, which connects to the air cleaner assembly that houses the air filter. The IAC valve is a small cylinder, about three to four inches in length and about an inch in diameter. It has a slightly smaller cylinder on top with an electrical connector at the end. Two bolts secure the valve to the throttle body. Unplug the IAC valve electrical connector.
Leave the engine idling, disconnect the vacuum gauge from the vacuum hose and plug the hose with a suitable nail or similar object. If the engine will not remain idling without the IAC valve connected, ask an assistant to depress slightly the accelerator to keep it at idle.
Connect a hand-held vacuum pump to the fitting of the EGR valve where the vacuum hose connects. Apply 10-inch Hg (34 kPa) of vacuum to the EGR valve. The engine idle should drop below 100 rpm and return to normal when disconnecting the vacuum pump from the valve. Otherwise, turn off the engine, remove the EGR valve and clean any carbon build up in the passages. Repeat steps 4 through 6. If you find no carbon buildup or the valve fails again the test after cleaning the passages, replace the valve.
