GM Cavalier/Sunbird/Skyhawk/Firenza 1982-1994

Idle Speed and Mixture Adjustments



All carbureted vehicles are equipped with an Idle Speed Control (ISC) motor which is in turn controlled by the Electronic Control Module (ECM). All idle speeds are programmed into the ECM's memory and then relayed to the ISC motor as any given situation requires. Curb idle is pre-set at the factory and not routinely adjustable. Although curb idle is not to be adjusted under normal conditions, it can be adjusted, but only upon replacement of the ISC (for further details, refer to Fuel System ).

The idle mixture screws are concealed under staked-in plugs. Idle mixture is not considered to be a normal tune-up procedure, because of the sensitivity of emission control adjustments. Mixture adjustment requires not only the special tools with which to remove the concealing plugs, but also the addition of an artificial enrichment substance (generally propane) which must be introduced into the carburetor by means of a finely calibrated metering valve. These tools are not generally available and require a certain amount of expertise to use, therefore, mixture adjustments are purposely not covered in this repair guide. If you suspect that your car's carburetor requires a mixture adjustment, we strongly recommend that the job be referred to a qualified service technician.


The fuel injected vehicles are controlled by a computer which supplies the correct amount of fuel during all engine operating conditions; no adjustment is necessary.