Rochester E4M Series

Fig. 2 Typical Quadrajet E4M series carburetor:

The E4M series (E4MC and E4ME) carburetors are used on vehicles equipped with the C3 (Computer Control Command) System, Fig. 2. An electrically operated mixture control solenoid is mounted in the float bowl and is used to control air and fuel metering to idle and main metering systems of the carburetor. Fuel metering is controlled by two special stepped primary metering rods, operating in removable jets and positioned by a plunger in the solenoid which is controlled by an electrical signal from the Electronic Control Module. Air metering to the idle system is controlled by an idle air bleed valve located in the air horn, which follows movement of the mixture control solenoid plunger to control the amount of bleed air into the idle system. A throttle position sensor mounted in the float bowl, is used to electrically signal the Electronic Control module of various throttle position changes.
On some 1982-84 units, an Idle Speed Control (ISC) mounted on the float bowl is used to control idle speed. On these units, the curb idle speed is programmed into the Electronic Control Module and no attempt should be made to adjust idle speed. On some 1982-88 models an Idle Load Compensator (ILC) mounted on the float bowl is used to control idle speed. The compensator uses manifold vacuum to sense changes in engine load and compensates by adjusting curb idle speed. This unit should not be adjusted, unless if during diagnosis, curb idle speed is not within specifications.
On 1982-84 air conditioned models, not equipped with ISC or ILC and all 1985-88 models not equipped with ILC, an Idle Speed Solenoid (ISS), mounted on the float bowl, is used to control engine curb idle speed. On 1982-84 models, the ISS is energized whenever the A/C compressor is engaged. On 1985-88 models, the ISS is actuated by a relay that is controlled by the ECM during two different modes of operation:
a. On models equipped with A/C, the ISS plunger will extend when the A/C switch is On to maintain curb idle speed.
b. On all models, the ISS plunger will extend during certain deceleration modes (above 40 mph) to maintain emissions.
On all models, the ISS is adjustable.