Lack of fuel causes pinging and then stalling.
Lack of power can be lack of air flow in, low compression or lack of "outflow"(exhaust blockage).
Check air filter and air tubes for blockages
O2 sensors should be changed every 100-150k miles, no it won't cause low power, it can cause rich running or pinging.
It doesn't have that much control of air/fuel mix, especially in '86
MAP sensor is the main air/fuel mix sensor in '86, these rarely fail, and idle would be poor
If you have an EGR system it can effect power but idle should be effected as well.
$25 vacuum gauge can tell you engine condition, if exhaust is blocked or compression is low.
Very good tool to have in the box, along with Volt/ohm meter
Vacuum gauge testing here:
http://www.gregsengine.com/using-a-vacuum-gauge.html
Any gas engine is still a gas engine no matter how many sensors or controls they add to the outside.
Whether it is 1 cylinder or 16 cylinders, a vacuum gauge is still the first tool I reach for most of the time.
Also just a heads up, the throttle cable can stretch after 30 years of use
With engine off press gas pedal down to the floor and put something on it to hold it down, or a stick against the seat works.
Now go to the engine and check if the throttle can be opened more at that end, if so, then you are not getting full throttle with the gas pedal.
Google: Ranger throttle cable mod
Easy fix if needed
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