An RS1800 ECU obviously isn't the right one for the car but wouldn't make it idle like that, my mate and I have just done a 2L conversion on his with one of my 1.8 Zetec ported/raised comp heads on it that's only running 1.8 management for the moment which isn't ideal by any means but it doesn't pink or anything, sounds sweet.
Does it idle or does your foot have to be on the accelerator?
It sounds very much like an air leak, it would cause it to do everything you're saying, when you're driving does it still sound like a pile of crap or is it fine?