93 5.7ltr code 35? Check engine light on at idle

93 Chevy truck with the 5.7ltr. It blinks a code 35, but no 35 is listed in my manual..what's the deal? The problem is that the check engine light comes on at idle, but goes out again if you take off, or rev up the engine for a couple seconds. I'm guessing the cat must be clogged, but thought I'd ask some of you guys that do this for a living, rather than a hobby, like me:)

Thanks!

could be the cats, but you might check the oxygen sensor.