91 Toyota 4Runner - some advise needed

Hey there! It seems my earlier post didn't come through very well....I have a 91 4Runner V6 automatic and it starts up normally and idles normally. After a while, it idle speed drops to about 500 RPM and the engine hesitates unless I maintain the RPM at about 2000 RPM. Spark plugs are new, hasn't been much more than 2 months since I replaced them, the cables are new and the air filter is clean. Any advise would be appreciated.