What does the idle speed control system do?

It prevents poor battery charging and erratic idling when clearance lamps (M/T model only), headlamps, or the rear defogger are operating. Proper fuel is added to keep a constant idle speed when the solenoid valve attached to the carburetor is in the "ON" position.

Where is the engine rev unit installed?

According to the diagram footnote, the engine rev unit is installed under the driver's seat.

When does the idle speed control solenoid valve operate?

It operates when at least one switch (lighting switch or rear defogger switch) is ON, and does not operate when all switches are OFF.

How does the A/T model differ from the M/T model in this system?

The A/T model includes an inhibitor relay between the engine rev unit and the solenoid valve, and its lighting switch input is low beam only, whereas the M/T model uses clearance, low and high beams.

What inputs feed the engine rev unit?

The ignition signal, the rear defogger switch, and the lighting switch (clearance, low and high beams on M/T; low beam on A/T).

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Nissan Micra Idle Speed Control System Diagram - Solenoid Valve Operation (EF & EC-19)

Idle Speed Control System schematic for M/T and A/T models, Nissan EF & EC manual

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Idle speed control system schematic: engine rev unit, idle-speed-control solenoid valve and mixture-bypass passage add fuel to hold idle when lamps or rear defogger load the system.

AI caption June 2005 · Photo 119 of 412

This document is a service manual page titled "Idle Speed Control System" describing how the system prevents poor battery charging and erratic idling when electrical loads are operating: clearance lamps (M/T model only), headlamps, and the rear defogger. It explains that proper fuel is added to maintain a constant idle speed when the solenoid valve attached to the carburetor is in the "ON" position. Two schematic diagrams are shown, one for the M/T (manual transmission) model and one for the A/T (automatic transmission) model. Both diagrams show the ignition signal feeding an engine rev unit (noted as installed under the driver's seat), which controls the idle speed control solenoid valve on the carburetor, with a mixture by-pass passage, fresh air inlet, fuel supply, and intake manifold labeled. The M/T diagram uses inputs from the rear defogger switch and lighting switch (clearance, low and high beams); the A/T version adds an inhibitor relay and uses the lighting switch on low beam only. An operation table summarizes logic: if at least one switch (lighting or rear defogger) is ON, the solenoid valve operates; if all switches are OFF, it does not operate. The page is stamped SEF054D and numbered EF & EC-19.

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Frequently asked questions

What does the idle speed control system do?: It prevents poor battery charging and erratic idling when clearance lamps (M/T model only), headlamps, or the rear defogger are operating. Proper fuel is added to keep a constant idle speed when the solenoid valve attached to the carburetor is in the "ON" position.
Where is the engine rev unit installed?: According to the diagram footnote, the engine rev unit is installed under the driver's seat.
When does the idle speed control solenoid valve operate?: It operates when at least one switch (lighting switch or rear defogger switch) is ON, and does not operate when all switches are OFF.
How does the A/T model differ from the M/T model in this system?: The A/T model includes an inhibitor relay between the engine rev unit and the solenoid valve, and its lighting switch input is low beam only, whereas the M/T model uses clearance, low and high beams.
What inputs feed the engine rev unit?: The ignition signal, the rear defogger switch, and the lighting switch (clearance, low and high beams on M/T; low beam on A/T).