what causes my 1990 4 runner to have no engine power
Very broad question. It could be anything from bad gas to a clogged catalytic converter.
I would go through it and give it the super tune up. New plugs, wires, cap, rotor, air filter, fuel filter. Then take the throttle body off and give that a good cleaning along with your Idle Air Control Valve. If unfamiliar with cleaning those items, check Youtube. Tons of videos. Also replace your PCV valve and check all lines for vacuum leaks. See how she runs then.
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