4runner mystery problem

[rainman0915]

I have a 91 v6 4runner 5 speed and yes i know they are inherently slow however...

This one is extremely sluggish uphill.

whenever you push it too hard it starts giving less and less power. its extremely unpredictable, some days on a given stretch of highway it will top out at 75 other days on the same stretch of highway it will top out at 50 in relatively similar weather conditions. i am baffled by this weirdness. i replaced the fuel filter which helped but there is still a serious issue, it almost feels like its a computer issue because when you push it too hard u can feel it flutter giving more and then less and then less power. its very hard to describe the feeling. anything above 3/4 throttle causes this issue, its almost like a runner hitting the wall

any ideas on what this could possibly be?

 

[mojo34]

A plugged catalytic converter will give these same problems.

 

[brownshoes]

several options:

plugged cat as mojo mentioned (easily tested by driving in 2nd gear, mid revs for @ 5 minutes, climb under and see if it is glowing redish. (not all together scientific but it did help me diagnose my vw a few years ago)

plugged air filter/ air inlet. Make sure your intake system is free and open (mouse nest, dead bird, anything in the chain

computer related issue. same vw had one bad computer box that we could only diagnose with the use of a hair dryer (heat the box to simulate road and engine heat and it would fault out).

balance of fuel system issue. Clogged injector, fuel line, fuel line screen (if there is one)

typically the big two, fuel and air, are easier to diagnose. the other item would be spark (plugs, wires, computer related).

good luck