The exhaust gas recirculation valve, or EGR valve, recirculates the exhaust gasses in the Isuzu Rodeo for more complete burning. The valve itself opens and closes to allow the exhaust gases to be burnt more thoroughly. However, when the valve stops opening on the exhaust cycle, then you may notice the engine idle drop. You may have significant idle problems with the Rodeo if the valve fails completely. Checking the EGR valve is easy, but you'll need an assistant to help you.
Start the engine. You may want to have an assistant do this for you. Have your assistant rev the engine.
Check the movement of the EGR plunger on the valve. The EGR valve on the Rodeo is on the left side of the engine near the firewall. You should be able to easily see the valve plunger opening and closing as your assistant revs the engine. If the valve is not opening, the valve has failed or is malfunctioning and needs to be checked and cleaned, or replaced.
Shut the engine off. Remove the two screws that hold the Rodeo's EGR valve in place and pull the EGR valve off.
Spray the end of the valve with carburettor. Carburettor cleaner is used to clean carbon deposits off of many different engine components. EGR valves may malfunction due to excessive amounts of carbon build-up so you need this type of cleaner to remove them.
Work the pipe-cleaner wire brush in and out of the valve opening. Make sure that you clean all of the carbon out of the valve opening.
Reinstall the EGR valve, tighten the screws and repeat steps 1 & 2. If the plunger on the valve is still not moving, the EGR valve has failed and needs to be replaced. If it moves once again, then the valve was simply dirty.