I recently came across this and did my research both on here and on various other forums.
Some said that it has to be programmed by a dealer/locksmith and some said that only the keys with a small dot near the end of the key blade works. Some also mentioned that walmart/home depot would cut the key.
However most of those information might not be the truth based on my experience. I'm willing to provide a small guide on this for those in need.
How to get a key blank
I bought the key blank from a seller on Amazon and there was no small dot on the key blade at all but it works.Those found on ebay might also work.
So just buy the cheapest one which says "for 03-09 4runner"
Should be less than 20 bucks shipped.
How to cut
I at first went to walmart but they refused to cut it because I didn't buy the key blank from them. Home depot and lowe's did the same thing.
So I asked a local locksmith and he did it for just 5 bucks. (just FYI those keys are made of brass, not steel, so most locksmiths would be able to cut them.)
How to program
Actually it's a super easy if you still have one master key that can start your 4runner. There was a pdf somewhere about how to do it on a Prado but
its not very clear(it would ask you to remove the key from ignition 3 times without mentioning putting it back in at all
) so I'll try to provide a clearer one here:
1. Take the new key and one master key that can start your 4runner(old key) into the 4runner with you and close the driver's door.(immobilizer light should be blinking)
2. Insert old key, remove old key, Insert old key, remove old key,
Insert old key, remove old key, Insert old key, remove old key,
Insert old key (immobilizer light should be off from the first insertion)
3. open and close driver's door six times (immobilizer light should be off)
Step 2 and 3 need to be done in less than 35 seconds(pdf says 35 seconds)
4.remove the old key. (immobilizer light should come on(steady on, not blinking))
5. insert the new key(immobilizer light should be blinking)
Then just sit there and wait, after about one minute the blinking immobilizer light should go off and you're done.
Whole process need to be repeated for any additional keys, the just programmed key could be used as the "old key" for the additional keys.
If there are 5 master keys registered with the immobilizer, it won't accept any more(and I don't know how would it tell you this, so just do a erase if you can't get it to work after trying for a few times). You have to erase them using a similar method(bring in just an old key, insert+remove one more time and open+close one more time, after the 7th close of the driver's door the immobilizer light will stay lighted for one second, remove the old key quickly after that and all but that one you just removed are erased.)
If you don't have any working master key(meaning you only have valet keys). Then I've no idea what could you do other than ask for help from a dealership.
Total cost is less than $25 if you still have at least 1 working master key. Less than 1/5 of what my local dealership wants.
Hope this would be useful for those in need, please post your results if you decided to give this a try.