its name —"Idle Air Control" says it all. It allows the ECU to maintain (control) the idle speed under various load and temperature conditions.

"..and what happens if it goes?" It shouldn't be a disaster, but depending on the variables above, the idling speed won't be correct for the existing conditions.

If the throttle linkage is in proper adjustment, the IAC can be fully shut, and a warm engine should still idle, but more slowly—at the "Baseline" idle speed of about 700 rpm.

This is how the base idle speed is set—by electrically shutting the IAC, then making a mechanical adjustment.
--
Bruce Young,
'93 940-NA (current)
'80 GLE V8 (Sold 5/03)
'83 Turbo 245
'76 244 (lasted only 255,000 miles)
73 142 (98K)
'71 144 (track modified--crusher bound)
New 144 from '67 to '78
Used '62 122 from '63 to '67

This allows a metered amount of air to bypass the throttle plates in a fuel injected engine. More air = higher RPM for cold start, or more power to compensate for increased load...Drive engaged, AC, power steering, etc.

Hello,

It bears the very small responsiblity of allowing bypass air so that your brick can idle while the throttle body is closed. It goes = no more idle.

Happy Bricking!!!

Richard

87 245 DL 373,000 km
82 242 GLT 121,000 km