Toyota Repair: fast idling 89 toyota pickup, air fuel mixture, 4x4 toyota

Question
My 1989 4x4 toyota pickup idles fast at all temp ranges. the milage is less than I expected at about 14-15 mpg. If I drive for twenty minutes or more the check engine light comes on and when checked the codes if displays are 25 and 26. Also the exhaust smells too rich. where is the best place to start I recently puchased this pickup and don't know much of its history.  

Answer
The codes 25/26 indicate a rich/lean condition, this code is set by the oxygen sensor because it has to constantly try to compensate for a problem with the engine's air fuel mixture, most of the time this is caused by an engine misfire or blown headgaskets if it's a V-6,or low compression on one or more cylinders and possibly a tight valve.
You need to check the basic functions of the engine:
Cylinder compression(this is the first step, if it is good there are other possible causes)
Electrical misfire
Possible blown headgaskets
The idle speed is irrelevant except that I think someone deliberately set it too high too mask a rough idle condition.