What engine do you have? that will make a difference in difficulty.
I have a six cyllander and all in all it took about 6.5 hours. However, When I pulled the plenum off I went ahead and replaced a bunch of other stuff too.
Valve Cover Gaskets
Plenum gasket
Plugs
Plug Wires
Plug Gaskets
Cleaned out Mass Air Flow sensor
I also was able to clean some of the built up sludge that had formed over the years.
Take a look
here or click the link in my sig. Under "engine" section is a good write up including some of the other things I did.
If your going to spend the time to do it, go ahead and do it right and change these other things.
I think i spent a total of $100 maybe? cant remember now.
Ks
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1997 4Runner - 4WD 3.4 V6 Limited - Anthracite Metalic
3rd Gen Tutorial and Doc Reference