Hey, I just got done with dealing with this exact issue in my 4Runner. 1997 SR5 140,000 miles. Mine started acting up a few months ago. I went and got a new key cut from the key code and this worked a little only that the key was almost inpossible to remove from the ignition. I kept using my old key that was easy to push in the ignition and remove from the ignition, but it would not turn most of the time. As time went on it got harder and harder to start / turn the ignition. It was to the point I thought it would not start and leave me stuck somewhere. Anyway, to get to the point, the ignition cylinder was worn out and needed to be replaced. The local dealership wanted $250-280 to replace it. They dont even do the work themselves, the sub it out to a lock smith. I ended up buying the ignition cylinder key set from the dealer for $104.62 before tax, you can find this part cheaper at Auto Zone or some other parts dealer, and I replaced it myself. If you have a Hanes or Chilton repair guide it will give you step by step instructions to replace it. It is very easy though. It took me about 10 minutes.
Step 1 - disconnect the battery so you do not risk setting off the air bags since you are workin gnear the steering column
Step 2 - remove the 4 bolts from the lower portion of the dash and drop the panel.
Step 3 - put the steering wheel in the lowest position
Step 4 - pop off the little bezel around the ignition
Step 5 - insert key and if possible turn it to the acc position
Step 6- insert a small screw driver in the hole in the underside of the ignition and pull out the entire assembly with the key.
Install of the new cylider is just the opposite.
Now, with the new ignition cylinder you will have new keys and it will not match your old key. The lock smith here in town told me he could rekey the ignition for $25. So, instead of being out $250-280 it cost about $113 for the ignition and $25 to rekey. `