Engine Service Light unlike other threads

Any help any one can give me to help with this problem I am having will be greatly appreciated.Here goes.The other day I was in a spot where my Delta 88 just died and because of the excessive age & mileage I decided to send it to the bone yard.Then I cam across a 1996 Pontiac Grand AM SE w/2.4 DOHC mileage was right around 100k but ran great and body is solid.So I bought her mainly needed wheels quick. (Perhaps that was the start of my problem)Any ways the Service Engine light has come on and the ETS light is on also I notice that occasionally while driving at night the headlights go off and then back on sometimes they stay off for 10 -15 seconds then come back on.I read through just about every thread on this Grand Am sight and found that sometimes the Service Engine light and ETS light will come on because of a burned out light. (Made Sense)I checked all the lights and replaced the one's that were out.Still having the headlight problem and Service Light w/the ETS light problem.Now the issue with the head lights I can deal with and if I don't use the auto light and manually turn them on thus far have not had them go out if I turn them on manually. Only seem to have that problem when I use the auto on feature. But the issue with the Service Engine & ETS light is driving me crazy. Again from reading the posts here I have not been able to find any that seems to be the same as mine.This is what I have done.I took the car too my mechanic and he read the code it said that I needed a new catalytic converter. He cleared the code and the lights went off and they stayed off for about 300 miles then it came back on.Being frustrated and trying to avoid paying $600 +/- for a new cat I thought well I can just buy a code scanner for myself and erase the codes and possible get a sticker. (WRONG ANSEWER NEXT CONTESTANT)This is what happened when I read the codes they said that I had a problem with the (evap & catalytic converter) so I erased the code and thought I would have about another 300 or so miles before they need to be erased again (For I still did not get my sticker yet lights came on before I could get the inspection station)Any How after erasing the codes the lights went out and I thought all was like before (Wrong)The lights came back on with in about 3 - 5 minutes. I read the codes again but this time is came up as P0440 = evap Emissions System Malfunction.Since this I have driven approximately 150 to 200 miles and have erased the code at least 4 times just trying to see if I could get the lights to stay out so I can get my sticker.The strange thing is that the Catalytic converter error has not shown back up in the error code just the evap.Do I really need to break down and buy a new catalytic converter or is there something else going on that will cause the catalytic converter to become an error if I do not erase the code and let the evap error stay for a while will the catalytic converter error show back up? I am really baffled with this now I do not claim to be a mechanic but I am a computer geek and one thing I know is that when programming code one error can cause several errors to show up. And by fixing the first error generally 80 - 90 % of all the other errors go away never to return until you mess something else up in the code.This is why the Service Engine & ETS lights coming on with a bulb being burned out made sense. However, I do not believe this is the issue considering every single light that I could see that did not work is working now or at least Ohm out as being good.Some assistance with this please.Thanks.Jay.

The P0440 code could be set by the EVAP cannister's purge valve solenoid not working properly or the vacuum hoses could have a split in them. Check out your EVAP cannister. It's responsible for collecting fuel tank fumes and feeding them back into your intake once your engine warms up.