HIGH PERFORMANCE TUNING KNOWLEDGE

Posted on by Gerrot Jacobson

Using Throttle Cracker to Drop Hanging Idle

 

Tech Tuesday: Hanging Idle – Gen 3 Fix – Throttle Cracker

by Gerrot Jacobson

 

You cruise slowly into the parking lot with all your buds, ready for that idle to drop and chop, but it doesn’t. You look a fool, and your car sounds just ok-ish. A short time later when you come to a complete stop, the idle drops and starts chopping harder than Mr. Miyagi. Why won’t this idle just drop and chop? Have you missed a step? Well, look no further. 

 

We hear this question all the time, “My idle hangs and won’t drop right away.” In automatic transmissions, this can make the car lurch forward or pull. In manual transmissions, it can do the same, exaggerate, and idle higher. What is happening here is the PCM is adding airflow via vehicle speed. The IAC will open a predetermined amount based on vehicle speed, causing the rise/hang in idle.  This is largely unnecessary and was used in older calibration strategies. 

 

Enable / Disable SpeedThere are a few ways to cure this symptom-based problem. The first and simplest way is to turn the Throttle Cracker off. All you need to do is change the enable speed/disable speed to something very high, such as 100mph/98 mph, so the car doesn't have the chance to use this airflow adder. 

 

Airflow TableThe second way to do this is to adjust the Throttle Cracker airflow table itself. If you look at the table, you will see larger numbers as vehicle speed and RPM increase. Zero the airflow additions to the 1,600 and lower RPM range, and whatever speed you are having an issue. For example, if my idle hangs badly under 32 MPH, lower the airflow numbers to zero in the 32MPH, and 1,600 RPM range and down as shown. 

  

There you go. Two super simple ways to fix your hanging idle so you can get that super sick chop out of your GEN III. 

 

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