2000 buick

lasabre has a rough idle and bad gas mileage. installed a new egr valve and a pcv valve. I still have a rough idle. any suggestions?

Do you have any codes? Have you checked all vacuum lines & cleaned Idle Air Control (IAC)? What about the plugs & wires, when was the last time they were changed? A lot of unknowns here.

Ran a scan twice; no trouble codes. Plugs and plug wires were replaced 20,000 miles ago. fuel filter and fuel pump were replaced in March, 2011. New battery in April. new oil, new oil filter and new air filter were install 2 weeks ago. Have not checked or cleaned the IAC. will do that tomorrow.
Thanks for the input.