GM Prizm/Nova 1985-1993 Repair Guide

Choke Opener System

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OPERATION



See Figures 1 and 2

The choke opener system, after warm-up, forcibly holds the choke valve open to prevent an over-rich mixture and releases the fast idle cam to the 3rd (lowest) step to lower the engine rpm.

When engine coolant temperature is below 122°F (50°C), the thermostatic vacuum switching valve connects port J to port M which places atmospheric pressure on the choke valve. Through the choke opener linkage, the fast idle cam is set at the first (high idle) or second step.

When the coolant temperature exceeds 154°F (68°C), the TVSV connects Port K to Port M which now applies manifold vacuum to the choke opener diaphragm. This action opens the choke valve further and releases the fast idle cam to the third step and idle speed decreases.



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Fig. Fig. 1: Choke opener system operation



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Fig. Fig. 2: Choke opener system operation

TESTING



Choke Opener System Operation
  1. Disconnect the vacuum hose from the choke opener diaphragm. With the coolant temperature below 122°F (50°C), step down on the accelerator pedal and release it.
  2.  
  3. Start the engine.
  4.  
  5. Reconnect the vacuum hose and check that the choke linkage does not move.
  6.  
  7. Warm the engine to normal operating temperature and shut it off.
  8.  
  9. Disconnect the vacuum hose from the choke opener diaphragm.
  10.  
  11. Set the fast idle cam. While holding the throttle slightly open, push the choke plate closed and hold it closed as you release the throttle.
  12.  
  13. Turn the key and start the motor but DO NOT touch the accelerator pedal.
  14.  
  15. Reconnect the vacuum hose. The choke linkage should move and the fast idle cam should release to the third step (lowest rpm).
  16.  

TVSV

For testing procedures for the TVSV please refer to the EGR system testing procedures earlier in this Section.

Choke Diaphragm

Check that the choke linkage moves in accordance with the amount of vacuum applied. If a problem is found, replace the diaphragm.

 
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