1991 toyota pickup truck...very unsteady idle?

vacuum leak?

idle air controller?

First, go to a do-it-yourself car wash, and power wash your engine bay, especially the space between the radiator and A/C condenser. This will improve air flow and also give you a clean work space. Then, buy a can of Gum-out, and spray all around your intake manifold and throttle body with the engine running. If there is any kind of external leak, the spray will cause you idle speed to change and voila, you have figured out where to concentrate your labor. Also, with the spray, clean out the throttle body, idle air control valve, and PCV hose. Idle speed is controlled by temperature and by the computer. Also, make sure that the battery cables are perfectly clean on BOTH ends. Voltage inconsistencies will invariably cause troubles like this. Good Luck!!!

ok my first guess is that one of your spark plug wires is pinched. check the wires to see if theres and rubber missing and the slightest amount of wire isnt ocovered too. im not sure if the spark plugs would do this. if its been a while since you changed them that might help. also it might that your pulley or your water pump isnt working right. good luck