An IIL is really just a permit to drive while you are still suspended. If you drive anywhere, including out-of-state, without a functioning IID in your car, you are not in compliance with your IIL and you would be driving while suspended. If you keep the IID in your car, there should be no problem in driving in another state, since you would still be complying with your IIL.
The only real additional restriction on an interlock Ignition license, as oppossed to a regular license, is that you can only drive a vehicle with a properly functioning interlock ignition device installed.
Yes, as far as Washimgton law is concerned. You may wish to double check with a lawyer from the States to which you are traveling.
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