Engine Computer Problems?

Has anyone else had "engine computer" problems? My lights been going on in my 99 corrolla and at first the service center claimed it was a faulty valve switch. After replacing it the light came back on the next day, now they say the engine computer is going out. The car has 84,000 miles on it.

Its this a common problem? How hard is it to replace?

The dealer is saying it's covered by a 8 year 80,000 mile warranty which I just went over.

Any help??

i would imagine it's not too common seeing as how you're the first person i've heard of it happening too. i'd take it to a few different places and have them look just to make sure the place you've already gone to isn't trying to screw you over