vethane

Hi everyone, i bought a gs300 and the day i got it the ecu fried itself, i replaced the ecu with an ebay ecu and master key and it was turning on fine but now every time i go for a drive itll start fine at my house then if i turn it off any where itll activate the kill switch anti theft and it needs to sit for a few hours until i can turn it back on. Not sure what the issue could be at all, i called lexus and they said they have no idea what the issue could be either and didnt want to throw parts at it
Thank you in advance for any help