RX300 ignition key, ECU?
 

Your ecu can be flashed and keys cut from either your vin or the code on the passenger side door lock. It would be easier than changing all that out. The key transponder code is registered in the ecu. Try a locksmith.

Here's a link to getting the key code. With the key code, you can have a key made on eBay from a seller name 1010keys. The usb cable that I purchased from Amazon is 'mini VCI'. It will include a copy of Techstream. https://www.clublexus.com/forums/rx-...l#post10137167

is there only one transponder frequency? I am seeing a key with 312 MHZ 4C chip but it also says compare number on your key (I have none) Will a locksmith know the frequency simply by the key code?
Also, I just got the techstream cable and software. is it easy to do? I have a locksmith cut the key first, correct?
Thanks for the help!!!!! this might be easier than I was expecting

Hate to say it, but without a master key it wont be too easy. To add keys with Techstream you have to have a programmed master key.

I can help if you are confident removing and replacing a chip in your ecu. I can send you a preprogrammed eeprom that will virginize your immobilizer. I have been giving these chips away for Land Cruisers and LX470s. I will send you one for free if you would like. I made a video showing how to swap the chip I will try to figure out how to post it.

These keys are what I used for my daughter's 2002 RX300.

http://Keyless2Go New Uncut Replacem..._HiniCb3B56N7Q

Hope these links work. This is a couple of videos I made for the LX470, but it is done the same way for the RX.

Swapping the eeprom


Registering keys

This youtuber claim that this method will work with older Toyota. You can try to verify if it does work. I don't know if it really works. I have a copy of Techstream that will allow me to erase all the registered key and will register the current key in the ignition lock.

It might work, but I dont think it will. I tried this on mine before I flashed the chip with no luck. I think it is for cars after 2002.

With Techstream you have to have a master key that is already registered in the ecu to add or delete keys.

On cars after 2002 you can reset the ecu with techstream using a passcode.

@Talons24 did you get your eeprom changed to the one I sent? If so everything go ok?

Rx ignition keys
 

If it is a first generation here is what i did, my keys were stolen. I went to a lexus recycler and got an ignition that included the original key. And fortunately the same car still had the ecu that matched the ignition and chip into he key. Altogether it cost $200

Rx ignition keys
 

So to answer your question, the igntionnswitch has a sensor in it the corresponds with the ecu. If they dont match the car wont start. I got the run around about doing the whole flashing crap and the way i mentioned earlier turned out to be less time consuming and cheaper. After that u just have to o program the fob to chip that locks the doors so u can use that feature. Hope this helps good luck!

I learned how bad my eyes were getting and how good reading glasses work when I did mine. Keys registered ok?

This can be the easiest way if you dont want to get into the ecu. You only need the key and ecu though. You dont have to change out the ignition switch. You can get keys cut to your vin and just use the master that came with the used ecu to program the new keys. The key doesnt have to be fully inserted to use for programming, just enough to open the gate.

The only issue that I see with using another ECU is the VIN number is also stored with the ECU. The car will now have the wrong VIN number and some state might have an issue with it when you take it in for emission testing. I believe that replacing the IC 900 chip with a virgin chip is the way to go. The chip that you supplied is it Microwire eeprom 9356?