[ChevyTech]

A common cause of an idle that hunts up and down on these trucks is a lean fuel mixture, usually from low fuel pressure. The fuel pressure must be tested with the engine running. An IAC sticking and a worn distributor can also cause idle issues.

There are multiple failures that can causes the TBI trucks to have low fuel pressure other then the fuel pump.


The IAC (Idle Air Control) controls the air passing through a throttle pate bypass passage.

The IAC (and computer) control the idle speed.
The IAC (and computer) is what gives the engine a “fast idle” speed when started cold.
The IAC also supplies more air to compensate for the extra load when the A/C is on. If you have A/C and turn it on while listening carefully you should be able to here the IAC controlling the idle as the A/C clutch engages and disengages.


When the engine does start, does the engine have a fast idle that slows down as it runs? The IAC (idle air control) is what gives the fast idle speed when started cold.

Does the engine start well without the gas pedal being pushed down at all?