Toyota Repair: 92 Toyota Truck, V-6 eng., problems, mass airflow meter, exhaust valve seat

Question
Hi Ted;

I have a question about my 1992 Toyota Pickup Truck, extra cab, with a; V-6, 3.0 liter engine, 5 spd. transmission, truck has 155,000 miles on original engine.

I took good care of this engine, it does not burn oil, good compression, etc..., the problem I am having is that there's a power hesitation, lack of power during high speed, truck just "boggs-down", engine seems to not "put-out" anymore power at some point of the accelerator pedal, usually at @ 3500+ RPM. At occasions, when I back of the pedal, it seems to go faster/more power than stepping at the pedal all the way. It does not happen all the time, but most of the times.

The power hesitation started before I had done the complete headwork on it, which I figure the power hesitation would go away once the heads were done, (because of a leaking exhaust valve seat or "burnt valve"), so I have had a complete headwork done (includes valves, valve seats, head gaskets, etc...), new timing belt.

The head machining was done at a machine shop, and all the removal/replacement work was done by me. I made sure the "timing" is correct with the timing belt, distributor, etc... This is my third timing belt replacement on this engine.

The "fuel injectors" all check out good in reference to the factory manual I have on hand. Fuel filter was replaced last month, airfilter is clean. Catalytic converter is also new, spark plugs all new too.

I have check out the "mass airflow meter", per the manual, it seems ok, at fully closed position, and fully opened position. Except for some point in the travel of the "butterfly", it seems to "open-up" (in ohms), the manual does not mention anything about this, it just said it will "change in a wave pattern as the measuring plate slowly moves".

I don't know what else to check out, so before I throw more parts/money on this truck, I want to make sure it is the right one, the manual calls for these parts at fault;

-fuel pump
-fuel pressure regulator
-oxygen sensor
-throttle position sensor
-water temp sensor
-intake air temp sensor
-mass airflow meter
-etc....., these are not in the order of faulted parts

If you have had any experience on this type engine/truck, please advise me of my next move.
Thanx for your time!

toyota owner;

phil

Answer
The first thing I would do is to see if the fuel pressure doesn't drop when the problem happens, if the fuel pressure is good I would suspect that there may be a problem with the airflow meter.
Can you tell me what the reason was for the catalityc converter replacement.