Toyota Repair: 1994 toyota 4runner - bad oxygen sensor, cylinder head gaskets, fuel injector problems

Question
Hi Tedd-
Thanks for helping and listening.  I have a 1994 toyota 4runner, 2x4, 3.0L v6, 152000 miles, automatic.  I am having some issues with my car having sporadic idle, fluctuating from 1,500 rpm's or so to sounding like its about to die (i just usually put the car in neutral and keep the idle at about 2k).  
This is a fairly new problem, and it is just getting worst.  At first it would only happen when I start the car, until its warm, but now it is happening whenever I am at a stop light.  I replaced the fuel filter and spark plugs at about 139k when I bought the car, and have been replacing the oil every 4k after that.  I do believe that the Cylinder Head Gaskets was replaced in the recall back in 1994-95.  I have been pocking around the net trying to see if there are some people with the same problems, and I have seen that a lot of people have been having problems with their Oxygen sensor.  Could this possibly be the problem?  Is there anyway that I could test for it?  Another post that I read on the net suggested that the problem might be the fuel injectors were gettin clogged.  I have been splacing a fuel injector fluid into my car everytime I replace the oil, once again about every 4k.  I am really stuck, and would love some help.  
Thanks a lot
Reghardt

Answer
Neither one of those suggestions is correct, if there was an 02 sensor problem the check engine light would turn on but this is not the case is this correct?
Fuel injector problems are very rare.
It's much more common that the is some sort of intake leak so I recommend that all the hoses be checked incluing the large air intake hoses from the air filter to the throttle body, they can crack and leak creating idle problems, another possibility may be the EGR(exhaust gas recirculation) system, the egr valve may be staying open or sticking at times, they too can cause idle problem and will not turn on a check engine light, finally, if those items are not the cause, there may be a problem with the air flow meter which can fail without turning on the check engine light, it's very important that you let me know if the engine light is on because it changes everything.