Diacom readings for IAC duty cycle merc black scorpion 5.7

[monkstr6100]

Well I broke down and got a diacom program of my own. This thing shows EVERYTHING! My question is what should the duty cycle of the IAC be? At idle it's around 30% which I think is normal! but as I throttle up it increases with the throttle. At WOT it the duty cycle goes all the way up to 70-80%? Is this normal? I assume that the duty cycle reflects how far OPEN the IAC is? So it would go down to almost nothing at full throttle or anything over idle for that matter? I am seeing this wrong? Thanks guys. Zach J.

 

[Fun Times]

Duty cycle is basically an electrical measurement of how far open the valve is. The more open = higher duty cycle = higher RPM. So in theory, it's also like an IAC follower, it's open so that when you go from full throttle to closed throttle in short order the valve is already open to allow the needed air in so the engine will not die from lack of air due to an immediate closing of the throttle.

Here's a couple of quotes that may help too.

The IAC (valve) is a 12v sensor / circuit powered by the main power relay = (MPR). The PCM grounds the IAC valve to open in which allows more air to enter the plenum. The PCM ungrounds the IAC valve to close in which reduces the air flow into the plenum. This strategy of the IAC control is called pulse width modulation (PWM) not counts. it is measured in a form of a percentage. So 100% of pulse width modulation (PWM) means the valve is fully 100% open. As 0% (PWM) means the valve is fully 100% closed. The PCM & power from MPR basically tells the IAC what position to have the valve constantly to control proper idle at all times.

An IAC duty cycle controlled valve is fairly simple in operation. It consists of an electric motor coil winding and operates by receiving continuous rapid pulses by the ECM having a specific duty cycle (ON TIME). The longer the duty cycle (ON TIME), the more the IAC valve opens and hence the more bypassed air that the valve lets through, therefore raising the idle speed. This type of IAC operation closely resembles that of an injector. It is referenced on a scan tool as IAC %, not count. A high percentage indicates a longer duty cycle (ON TIME).

Here's a good read about the IAC if interested,
http://www.gmtuners.com/tech/TPS_IAC.htm