Idle Control Motor (Idle Stabilizer) Replacement

Procedure contributed by Terry and Donald Burnett.

Introduction

1985.5 and later 944s and all 944 Turbos use a DME-controlled electrically operated bypass valve — the idle control motor (also called the idle stabilizer or idle controller) — to regulate idle speed. This procedure does not apply to early 944s or 944S/S2 models, which use different idle control systems.

The idle controller regulates idle speed when the engine is cold or when A/C compressor or alternator loads are present. It does this by allowing metered air to bypass the throttle into the intake manifold. The DME activates it when the throttle position switch indicates a closed throttle. Idle speed problems can also be caused by vacuum leaks, an improperly adjusted or missing idle speed set screw, a sticking throttle plate, or a defective/maladjusted TPS — diagnose these possibilities before replacing the idle controller.

Symptoms of a defective idle controller:

• Idle speed drops when cold or under electrical load, causing stalling
• Erratic idle and a sucking noise (air leak through a failed controller body)
• Wiring broken or shorted near the controller plug, or connector fallen off

Tip: An old method for locating vacuum leaks is to carefully spray starting fluid (ether) near suspected areas — RPM will momentarily increase as the ether is drawn in and burned. Starting fluid is highly flammable and potentially explosive; use with extreme care.

With the intake manifold removed, inspect all accessible hoses, coolant lines, and other buried components. Replacing aged rubber items at this time avoids piecemeal failures later. The procedure can be completed with parts in hand in approximately two hours.

Note: Some owners have replaced the idle controller without removing the intake manifold by shearing off the rubber mounts and sliding the controller out, allowing the new unit to be held in place by its hoses only. This is possible but challenging, as access is limited and hose clamps may not be reachable.

Tools

• Standard mechanic's tools

Other Procedures Referenced

• FUEL-02 — Fuel Injector Removal
• FUEL-09 — Intake Manifold Removal
• BOLT-01 — Allen Head and Cheesehead Bolt Removal
• FUEL-08 — Idle Speed Adjustment

Idle Controller Replacement

1. With the intake manifold removed (FUEL-09), loosen the 13 mm bolt clamping the idle controller to its mounting bracket.
2. Loosen and remove the hose from the intake boot on the left-side connection of the controller.
3. Unplug the electrical connector.
4. Remove the controller by sliding it out of its bracket with the remaining hose still attached.

Note: If the rubber mounting isolators are broken, the controller and bracket will come out as a unit. Remove the broken isolator studs from the engine block and install new ones. Also remove the broken isolators from the mounting bracket.

5. Mark the orientation of the attached hose on the new controller body before installation so it can be reinstalled in the same position. Note the flow direction arrow on the controller body — do not reverse the unit.

6. Install the new controller into the bracket while reconnecting the second hose. Tighten hose clamps and the bracket mounting bolt. If replacing rubber mounting isolators, seat the bracket onto the new isolators and tighten the nuts.

7. Connect the electrical connector.

8. Install the intake manifold (FUEL-09).

9. Install the fuel rail (FUEL-02).

10. Connect the battery and start the engine. Check for vacuum and fuel leaks.

11. Verify idle speed is stable:

    • 944 (USA/Canada/Japan): 900 ± 50 rpm
    • 944 (rest of world): 800 ± 50 rpm
    • 944 Turbo (all markets): 840 ± 40 rpm

    Adjust if needed (FUEL-08).