Here's why:
* EGR's Role: The EGR system reduces NOx emissions by recirculating exhaust gas back into the intake manifold. This dilutes the air/fuel mixture, slightly lowering combustion temperature. A *stuck open* EGR valve might cause slightly lower idle RPMs (due to a leaner mixture), while a *stuck closed* EGR would have minimal impact on idle speed.
* More Likely Culprits: High idle in a 1996 Firebird is much more likely caused by issues like:
* Idle Air Control (IAC) valve: This is the most common cause of high idle. A dirty or faulty IAC valve can't properly regulate the amount of air entering the engine at idle.
* Throttle Position Sensor (TPS): A faulty TPS provides inaccurate readings to the engine computer, leading to incorrect fuel and air mixture adjustments.
* Vacuum leaks: Leaks in the vacuum lines can cause erratic idle and high RPMs.
* Mass Air Flow (MAF) sensor: A malfunctioning MAF sensor can cause incorrect fuel delivery, leading to high RPMs.
* Engine Computer (PCM): Though less common, a faulty PCM can cause various problems, including high idle.
In summary: While a completely malfunctioning EGR system *could* indirectly contribute to minor idle irregularities, it's highly unlikely to be the sole cause of significantly high idle RPMs. You should focus your diagnostic efforts on the components listed above before suspecting the EGR valve. A mechanic using a scan tool can quickly check for diagnostic trouble codes (DTCs) that might point to the actual problem.
