Using Holley's Terminator X Software To Better Control Ford's Idle Air Control Motor Behavior

By: Wes Duenkel | 05/04/2021 < Back to Motor Life Home

The Holley Terminator X is a tuning revelation for Foxbody Mustangs. The Terminator X makes it easy to accommodate major engine changes, power adders, and even simplify nitrous. But for all the ways the Holley Terminator X makes life easier for Mustang racers, some users struggle with the Ford air control motor (IAC) behavior. The combination of the Terminator X's simplified IAC settings and the Ford IAC motor's flow characteristics presents specific challenges—especially on stick shift cars.

Fortunately, there's a hidden gem in the Terminator X software to get your Terminator X-equipped Foxbody Mustang's RPMs settling down to idle softly and purring like a kitten: Advanced 1D tables. We'll show you how to get your Ford IAC performance on the path to idle nirvana.

TermX Ford IAC

The Terminator X is compatible with Ford's Idle Air Control Motor (IAC), which simplifies installation. However, the Ford IAC doesn't flow air in a linear fashion, which presents a challenge.

Creating a 1D table for IAC control will do three things: address Ford's non-linear IAC flow, work beyond the Terminator X's simplified IAC Ramp Down settings, and add a dashpot solenoid effect for manual transmission drivability.

Ford's Non-Linear IAC Flow

The crux of the matter is Ford's IAC doesn't flow air linearly over its operating range. There is little air flow change between 0% and 40% of the IAC's position. This means the IAC doesn't have any flow control when moving through this range—it's just wasted position and time before the engine responds to the IAC. Between 40% and 80% is the IAC's most linear range. Keeping the IAC operating above 40% will improve the IAC's ability to control the engine speed.

Fox TermX IAC position chart

This Holley data log scatter plot (using Holley's helpful Terminator X V2 software!) displays IAC Position versus engine RPM. Between 0% and 40% there is little change in the engine RPM. The most linear range is between 40% and 80%, which is where the engine responds best to changes in IAC position. We'll use a 1D table to limit the IAC position to at least 40% so the IAC can better control engine speed.

A workaround is to adjust the throttle blade so that the engine idles on its own without the IAC, but that still doesn't address that the IAC needs to move through ineffective range before it has any effect.

Terminator X's Simplified IAC Ramp Down Settings

The out-of-the-box IAC strategy in the Terminator X software is simple, but stick shift cars present a situation that affects drivability: in-gear deceleration. If the engine is in gear during deceleration for longer than the Ramp Decay Time, the IAC position goes to zero, even though the engine speed is well above idle. Because of the IAC's non-linear flow, the IAC needs to open all the way back to 40% until it's effectively adding airflow. The result is the RPMs drop quickly between gear changes, which can make gear changes rough.

Ford TermX IAC tuning screen

The Terminator's IAC settings are simple, however limit tuning that can be helpful in certain situations. We replaced the simplified "IAC Hold Position" and "Ramp Decay Time" settings with a 1D table.

Adding Dashpot Solenoid Effect

Before fuel injection was developed, many OEMs used a dashpot solenoid that would hold the carburetor throttle blades open slightly while driving. The added idle air flow slowed the RPM drop when the engine was unloaded, such as between manual transmission shifts. The Terminator X doesn't use a dashpot solenoid, but you can simulate the effect by using a 1D table.

Ford TermX RPM ramp setting

First, we zeroed out the "IAC Hold Position" and "Ramp Decay Time" settings and set the "RPM Above Idle to Start Ramp" to 2,000 RPM.

Ford TermX IAC config 2

Then, we went to Toolbox > Add Individual Config, selected "Advanced," and opened the "Default Adv.adv" file.

Ford TermX IAC config 3

We clicked the arrow to the right of the (new) Advanced ICF icon dropdown, and selected 1D Tables >Table #1.

Ford TermX IAC Config 4

Next, we clicked the "Enable Table" checkbox to edit the table.

Ford TermX IAC Config 5

Here's what we set up. This table modifies IAC Hold Position based upon RPM. (This is added to the IAC Hold Position in the IAC Ramp Down Settings, but since the IAC Hold Position setting is 0%, table represents the total IAC Hold Position.) Note that we selected the "Table Type" as "IAC Position Offset" and the "X Axis" as "RPM." This table sets an IAC hold position that decays based upon RPM, rather than a single set position that decays over time. This can yield smoother results with a manual transmission. Note that our target idle speed is 800 RPM, and the values ramp up on either side of that target. The lower ramp helps the IAC "catch" the engine if it drops below 800 RPM, and the higher ramp gradually closes off the IAC as the RPMs drop.

In practice, this table sets the minimum IAC position for the engine speeds shown. Higher values will make the RPM drop slower, and lower values will make it drop quicker. Keep in mind that if the values are too high, the airflow won't let the engine RPM come down and the engine speed will "hang." We found the best results using the highest values we could get away with before the engine RPMs hung. You'll also have to back off your throttle body idle screw to compensate for any additional airflow going through the IAC. As with any time you change the throttle blade angle at idle, don't forget to do a TPS Autoset!

Using a 1D table is a great way to tailor the IAC behavior to match your vehicle's needs and your driving tastes. It might take some experimentation to determine the right values and slopes in the table work for your setup, but the little bit of effort is worth the results.

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