Toyota: Check Engine Light on 88 Pickup, lean mixture, oxygen sensor

Question
Hi-
I have an 88 toyota P/U V6 EFI 3V-ZE engine. It has about 165K on her. My check engine light is coming on sporadically, especially when going up hills or on the highway. At low speeds or on flats it goes off, but it doesnt seem to be RPM related (I can rev the engine in place and the light doesnt come on) It also seems to come one more when the vehicle is warmed up. I love the red dragon, and it needs to last till I get out of grad school, and im broke, so your help is much appreciated.

Answer
Sorry for the late reply.  I was trying all day yesterday,  only to get errors everytime I pressed send.  Anyways, being that typically you get a engine code during load on the engine and especially when its hot, it could be your oxygen sensor or your exhaust gas temp sensor.  I forget specifically which one your engine has but they are only located in ONE place.  On the headers but before the end of the catylatic converter.  Your engine could be running a lean mixture and only when you are running under load does the computer see it happen.  Have you been keeping up to date with the truck's engine?  A proper tune-up will do wonders.  

(Motor oil and filter, spark plugs, spark wires, distributor cap & rotor, O2/Oxygen or EGT sensor, throttle body cleaning, PCV valve, fuel filter and a good fuel injector cleaner)

At the minimum, try a bottle of Seafoam in your gas tank (as per instructions), it's amazing.  Use it in your crankcase to loosen burnt motor oil off the crankshaft and through your brake booster vaccum line to clean off the carbon build up in your intake manifold.  

Sorry for the late reply and I hope this helps.