Look for hoses coming from the intake manifold's vacuum port(s). These hoses will likely be relatively thick and will branch out to several places. Key components to look for and trace hoses *from* and *to* are:
* Idle Air Control (IAC) valve: This is a crucial component for idle control. The vacuum hose to the IAC is usually a smaller diameter hose. The IAC itself is typically located near the throttle body.
* Brake booster: A large vacuum hose goes to the brake booster. While not directly controlling idle speed, a leak here will affect it.
* EGR valve (Exhaust Gas Recirculation): The EGR valve uses vacuum to control the amount of exhaust gas recirculated. A leak here will also affect idle.
* Distributor Vacuum Advance (if applicable): Older systems used vacuum to advance timing; though less common in 2000 models, it's possible.
* Throttle Body: Look carefully for smaller hoses on the throttle body itself, as some may control the idle air bypass or other elements influencing idle.
To find the idle-specific hoses, you'll need to:
1. Consult a repair manual: A Chilton's or Haynes manual for your specific year and model Grand Am will have diagrams showing the vacuum lines and their routing. This is the best way to pinpoint which hoses affect idle.
2. Visually inspect: Carefully examine the intake manifold and the components listed above. Look for hoses that are brittle, cracked, disconnected, or show signs of leakage.
3. Trace the hoses: Start at the intake manifold and follow each vacuum hose to its destination. This will help you identify which ones are involved in idle control.
4. Listen for leaks: With the engine running, listen carefully for hissing sounds near vacuum hoses, indicating leaks that might affect the idle.
Important Note: Working on vacuum lines requires care. Misconnecting hoses can lead to poor performance or even damage to the engine. If you're not comfortable performing this task, it's best to consult a qualified mechanic.
