1999 Buick Century

Engine Performance problem
1999 Buick Century 6 cyl All Wheel Drive Automatic 165000 miles

1999 buick century ck eng. Light came on-auto zone said it showed running lean, egr, and o2 sensor problems. Advised me to run inj. Cleaner and drive about 50 miles to take care of it. Did that-next day it ran like a wagon sometimes-no power on hills and has a slight burn rubber smell when I shut it off. Took to a repair shop-they say it is a misfire on 4 & 5, EGR, and o2 sensor. Could it be all these issues or is it possiblly the cat converter? Can't afford to take it to umpteen shops. Also, the CEL started flashing -was told I could drive it but it would be rough. Any ideas where I should really take it? I know its high mileage but can't replace it since I am currently laid off. Thanks for any suggestions.
March 11, 2010.

The flashing SES light would indicate a convertor problem.

If you can remove convertor (bolted on) look down convertor, if you see signs of overheating, melted material, chunks of material, the convertor is bad.

You must find cause, usually a rich fuel mixture, before replacing convertor.

Mar 12, 2010.