Trouble starting after sitting....?

Ok, I've got a 2002 alero and when it sits for about 4 hours, it wont start with out using starting fluid or carb spray. I've checked the fuel pressure and it checks out ok. I've changed the fuel filter and gave it a tune up, changing the plugs and wires. It runs prefect once it is started! Just can't leave it sit... Any help???:banghead: Thanks!

Ok, I've got a 2002 alero and when it sits for about 4 hours, it wont start with out using starting fluid or carb spray. I've checked the fuel pressure and it checks out ok. I've changed the fuel filter and gave it a tune up, changing the plugs and wires. It runs prefect once it is started! Just can't leave it sit... Any help???:banghead: Thanks!

do you have access to a ecm scanner?

No, I don't. Do you think it could be 1 of those sensors right around the fuel injection system? Because, like I said, it runs perfectly once it's started. I just don't get it! Thanks for your help!