My buddy has an 89 festiva, that runs rich, and quite honestly, has potential. But I can't seem to stop it, and the O2 sensor has been replaced. It runs great, but lightly smokes gray and chugs A lit.

I'm assuming this is the rare EFI/auto of that year. You might also check other inputs, like the coolant temp sensor and then I think there is an air temp sensor inside the front of the vaf that you can clean. I would also register on www.fordfestiva.com and ask for help, it is an awesome forum and has a HUGE following. They'll have much more info than me. Good luck and come back and let me know what it is.