Maintenance and Tune-Up - Idle Speed and Idle Air Control (IAC) Duty Inspection - 2015/07

Oct 23, 2026

Idle speed and Idle Air Control (IAC) duty inspection instructions define applicable models and serial number ranges and specify inspection timing. The procedure requires warming up the engine, confirming stable engine speed, verifying throttle/link smoothness, fuel injection and ECM wiring, ignition timing, tappet clearance, and absence of abnormal air intake. It then explains two adjustment methods using the SDS with service data/engine data, or using an IAC duty fixed mode via key start or keyless start to set duty and fine-tune rpm to specification.

LanguageEnglish

CategoryResearch & Report

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Pages5

Reading Time13 min

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Idle Speed and Idle Air Control (IAC) Duty Inspection (2015/07)

Applicable models and serial numbers

Pre-check conditions before inspection

Inspection methods (SDS vs IAC duty fixed mode)

Inspection and adjustment specifications

Normal key start model procedure

Keyless start model procedure

Maintenance and Tune-Up Service Instructions Idle Speed and Idle Air Control (IAC) Duty Inspection (2015/07) CENGG2110206019 Applicable Model and Effective Serial Number: 10003F-610001 and later, 11503F-610001 and later, 11504F-610001 and later, 11503Z-610001 and later, 14003F-610001 and later, 14003Z-610001 and later. Inspect idle speed and IAC duty Initially after 20 hours (1 month) and every 200 hours (12 months) NOTE Before checking idle speed / IAC duty, make sure of the following. • Engine must be warmed up. • Check idle speed after engine speed has stabilized. • Check throttle link mechanism and throttle valve for smooth operation. • Lead wire and hoses of electronic fuel injection and engine control systems are connected securely. • Ignition timing is within specification. • Tappet clearance is checked according to maintenance schedule. • No abnormal air drawn in from air intake system. After all items are confirmed, check idle speed and IAC duty. There are two methods available for performing the idle speed / IAC duty inspection and adjustment; 1) Using a personal computer and the SDS (Suzuki Diagnostic System) software. Suzuki recommends using this method as it is possible to monitor the inspection data. 1. SDS service connector IGG211020002-01 2) Adjust engine speed by the IAC duty fixed mode. In IAC duty fixed mode, engine speed can be adjusted while monitoring engine speed by tachometer. IGG211020001-03 SDS tool is used To perform the idle speed and IAC duty inspection, use personal computer and the SDS tool. 1) Connect the SDS tool to engine. Refer to the step 1 on the SDS operation manual. 2) Start the engine and allow to warm up. 3) Check the engine speed and IAC duty by using“Service data / Engine data”mode in the SDS. Idle speed in neutral gear (IAC duty) Standard: 650 – 750 r/min (Duty: Approx. 33%) NOTE During the period of idling or trolling the IAC valve duty is approx. 33%, however it varies by the load, climate, water condition, [etc. to](etc. to)[ ](etc. to)[keep the engine speed at preset value.](keep the engine speed at preset value.) 4) If engine idle speed / IAC duty is out of the specification, the following adjustment must be performed. a) Turn the by-pass air screw in an appropriate direction to bring it to the standard specification. NOTE Idling / trolling speed is controlled by the IAC system. Do not attempt to adjust the throttle valve opening by turning the throttle stop screw. IGG211020003-01 | 1. Throttle body | 2. By-pass air screw | | --- | --- | b) Shift into forward, check in-gear idle speed. NOTE • The IAC duty at the trolling speed will be increased more than that at idle speed due to the load. • Trolling speed (in-gear idle speed) is same as idle speed. • Idling / trolling speed of 650 – 750 [r/min. is](r/min. is)[ ](r/min. is)[controlled by IAC system.](controlled by IAC system.) If engine speed can not be controlled to the specification, IAC passage may be clogged or IAC system may not operate correctly. See “Idle Air Control System Description”in Section 1G in related manual. Idle speed in gear (IAC duty) 650 – 750 r/min (Duty: Approx. 25 – 36%) Adjust engine speed by IAC duty fixed mode (Normal key start model) For normal key start model, checking and adjustment of idle speed / IAC duty by IAC duty fixed mode are as follows; 1) Start the engine and allow to warm up. 2) Shift into Neutral and close the throttle fully (this will cause a fully close throttle signal to be input to the ECM) . 3) To set the IAC duty to constant 32 .5%, turn the ignition key from “ON” to “START” five times within ten seconds. At this time, caution buzzer will sound to notify that IAC duty is in fixed mode. NOTE | While IAC duty is at a fixed 32.5% duty, the“Check Engine” lamp will flash.
This function is added to “caution buzzer sound”. | | --- | | NOTE | | • The ignition key operat

FAQs

How often should the idle speed and IAC duty be inspected and adjusted?

Initially after 20 hours (about 1 month), then every 200 hours (about 12 months).

What pre-checks must be completed before measuring idle speed/IAC duty?

Warm up the engine, ensure engine speed is stabilized before checking, verify throttle link/throttle valve smoothness, confirm electronic fuel injection and engine control system lead wires/hoses are securely connected, verify ignition timing, check tappet clearance per the schedule, and ensure no abnormal air is drawn from the air intake system.

What should you do if idle speed/IAC duty is out of specification?

Adjust using the by-pass air screw to bring values into the standard range, then shift into forward to check in-gear idle speed. If speed cannot be controlled to specification, the IAC passage may be clogged or the IAC system may not operate correctly.

Oct 23, 2026

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