I picked up a 91 4x4 22re truck it runs great when cold but when warmed up its idle wanders up n down drastically. Upon cheking it out I found the 02 connector not connected to anything and can't find the connector it goes to? I'v tried tracing it from the ECU but not sure which one it is?

 

possible causes-
throttle position sensor
coolant temp sensor
faulty O2 (which could cover your situation)
vacuum leaks

have you tried pulling any trouble codes?

 

I really want to figure out where the 02 sensor connector is. The 02 sensor is on the exhaust mainifold and the wire is about 10" long, theres no other wire or connector within its reach?

 

on a 91, the O2 sensor should be under the cab in front of the catalytic converter... there may also be a 2nd one behind the converter. if you have one on the exhaust manifold, someone may have replaced the manifold with an earlier model one that has the sensor there, and left the sensor in to keep the hole plugged.
so, check under the cab and see what you have.