bad coil pack??? yr: 2000
 

ive known since i bought the car over 2 years ago that it needs a oxygen sensor but i still dont know which one.... the check engine light has always been on and ive been told its because of the sensor. about 3-4 months ago i over heated my engine while trying to get home. there was a hole in a hose so all of my coolant would leak out within minutes. it started as a minor hole so i would have to fill up my coolant maybe a couple times a month. then it went to a couple times a day until i was on my way home from my aunt and uncles house when it started smoking (white smoke. whatever you call that stuff. steam?) and so we replaced the water pump, the hose that had a whole in it, i previously needed a cerpintine belt and we replaced something else but i dont remember. so it ran ok for a couple months. then a month ago it started leaking coolant again. we looked at the water pump and from the outside it looked fine but apparently not so we had to replace that again. i have a new timing belt but i have to go get that put it and it would be 100 bucks for labor. i dont have the money right now for that. so this last saturday i drove to my boss' house to get my check. it was running as it always does, crappy. it wont go more then 20 mph unless it has been warming up for 10-15 minutes, then it still hesitates and jerks for a couple miles then it will go faster but it will still jerk a little if im pushing on the gas. so my car starts after i turn it off for about 30 minutes. i get about a mile down the road and its acting like its not warm at all then the check engine light starts blinking. its done that before but it usually stops after i let the car sit for about a minute. so i pull over and it continues to blink and my car is barely idling. so i tow it home and we do a test to get the codes to tell us what is wrong. the codes indicate to replace the sparl plugs and spark plug wires. we do and it doesnt work. still the same as before. is it the coil pack???? if so, where can i get a used one or even a new one for less? any ideas? anyone else have this problem?