For this vintage of truck - there are three possible places I'd check first. One is the idle adjustment screw - should be located very close to the throttle cam - they have a tendency to back out over time and mess with the idle. Other is close to the back of the engine - the EGR's plumbing, there is a place where a bunch of vacuum hoses plug into a valve - sometimes one of those vacuum hoses will be damaged, missing, or just got disconnected. Might just need a good throttle body cleaning - even a fairly small amount of varnish and gunk can cause idle issues.
Other than that - could be any number of things. Bad tank of gas, fuel line leaks, vacuum leak, exhaust leak, etc. But the above are pretty common the Toyota trucks.