I bought a 04 Pontiac Vibe that needed a clutch, and after installing a new one, engine idle was all over the place. I cleaned the throttle body and MAF sensor,and checked that Idle Control Solenoid was moving freely - no difference. I was contemplating replacing the intake manifold gasket, but I decided to check again for vacuum leaks. No leaks, but when I checked the vacuum hose routing diagram under the hood, I discovered that 2 vacuum lines were routed wrong, easy to do because they are the same size and in the same area. Switched them over and no more erratic idle.