my 91 4runner auto (180K) has 1100 rpm idle when at park but if you shift it to drive with foot on the breaks, it vibrates and idle goes down to 500. Just changed wires (oem), sparkplug (ngk grooved), and o2 sensor. Any idea whats going on?

 

i got the same issue....and i dont know either

 

Try cleaning the throttle body.Dont use carb cleaner get the throttle body cleaner made for this.Its a start.

 

try the idle control valve sensor?