DEF Idle Air Control Valve Motor IAC for MerCruiser ECM 555 (2001+) — Sierra 18-7701 / 862998 Direct Replacement with Gasket

DEF Idle Air Control Valve (IAC) 862998 / Sierra 18-7701 is a direct-replacement idle air control motor engineered to fit MerCruiser ECM 555 (2001+) and a wide range of Alpha and Bravo engines.

This replacement IAC motor from DEF restores precise idle airflow control on compatible MerCruiser powerheads. Built as a brand-new, high-quality unit, it comes with the required gasket and is intended to match the fit and function of original OE components for applications listed by Sierra part 18-7701 and MerCruiser part 862998.

Which engines and ECMs will this IAC motor fit?

This DEF IAC motor is designed for MerCruiser ECM 555 models from 2001 onward and fits many Alpha and Bravo models. It covers a variety of displacements and induction systems for broad compatibility.

• Compatible with MerCruiser ECM 555 (2001+)
• Fits Alpha 4.3L and Bravo 5.0L/5.0LX models
• Works with 5.7L 350 MAG, 5.7L Bravo EFI, and 454/502/7.4L/8.2L MPI/MIE engines
• Direct replacement for Sierra 18-7701 and MerCruiser 862998

How does installing this replacement IAC motor affect idle performance?

Replacing a worn or faulty IAC motor with this DEF unit helps restore steady idle control by regulating the airflow bypassing the throttle plate. Expect smoother idle transitions and more reliable engine speed management when the part matches the engine’s requirements.

• Re-establishes consistent idle airflow regulation
• Reduces hunting or unstable idle behavior
• Supports correct idle recovery after load changes

What comes in the box and what should I prepare for installation?

The product ships as a single IAC valve motor with a new gasket to ensure a proper seal during installation. Basic hand tools and a clean mounting surface are typically all that’s needed; follow manufacturer torque specs and electrical connector polarity when reattaching.

• 1 × DEF Idle Air Control Valve motor
• 1 × replacement gasket included
• Prepare screwdrivers, socket set, and cleaner for mating surfaces
• Verify connector pin alignment and ECM compatibility before installation

Will this DEF part meet OEM fit and durability expectations?

This unit is produced as a high-quality aftermarket replacement intended to replicate OEM fit and basic durability for the listed applications. It’s made for direct swap-in where the original part numbers Sierra 18-7701 or MerCruiser 862998 are specified.

• Manufactured as a brand-new replacement component
• Engineered to match mounting points and electrical interface
• Includes gasket to help prevent vacuum or coolant leaks at the mount

Who is this for: Technicians, boat owners, and marine service shops replacing a failing idle air control motor on MerCruiser engines that use ECM 555 (2001 and newer) will find this DEF IAC valve useful. Choose this unit when you need a direct-fit aftermarket alternative to Sierra 18-7701 or MerCruiser 862998 that ships ready for installation with a gasket and aims to restore proper idle regulation.