Closing in on a problem

**1great40** · 10-20-2014

Hi all. Today I installed the PROM that Eagle Mark cooked up for me, just to see how the truck would run. The good news is that it runs exactly like the stock PROM. The bad news is that it runs exactly like the stock PROM. The whole point in having the custom PROM was to have the idle set to 725 RPM. I know he addressed things like EGR, AIR, etc but I was disappointed that there is no change in the idle speed. I'm not sure what I'm missing here. What sort of magic does it take to change the idle speed? The odd thing is that when I first tried this prom, I was observing the RPM with an Actron scanner. That scanner only works in 10k mode. Mark told me he defaulted all the idle values to 725, that included the idle speed in 10K mode, which is usually 1000 RPM. When the scanner was attached, the engine idled at 725 RPM in park and 725 RPM in drive.

Anyone have any suggestions?

**dave w** · 10-20-2014

Originally Posted by 1great40

Hi all. Today I installed the PROM that Eagle Mark cooked up for me, just to see how the truck would run. The good news is that it runs exactly like the stock PROM. The bad news is that it runs exactly like the stock PROM. The whole point in having the custom PROM was to have the idle set to 725 RPM. I know he addressed things like EGR, AIR, etc but I was disappointed that there is no change in the idle speed. I'm not sure what I'm missing here. What sort of magic does it take to change the idle speed? The odd thing is that when I first tried this prom, I was observing the RPM with an Actron scanner. That scanner only works in 10k mode. Mark told me he defaulted all the idle values to 725, that included the idle speed in 10K mode, which is usually 1000 RPM. When the scanner was attached, the engine idled at 725 RPM in park and 725 RPM in drive.

Anyone have any suggestions?

The TunerPro parameter search shows about 20 idle parameters for the '7747 ECM. See attached screen shot. Usually the Desired IAC Idle C/L (closed loop) Speed table has the biggest effect on idle speed. I recommend an IAC minimum air adjustment of 10 ~ 20 steps prior to PROM chip changes.

dave w

**1great40** · 10-20-2014

Last time I checked my IAC count was about 12. How do I get to that screen you posted in Tuner Pro?

**dave w** · 10-20-2014

Originally Posted by 1great40

How do I get to that screen you posted in Tuner Pro?

Tools ... Parameter Finder ... See attached screen shot.

dave w

**lionelhutz** · 10-20-2014

Originally Posted by 1great40

Last time I checked my IAC count was about 12. How do I get to that screen you posted in Tuner Pro?

Ever try adjusting the idle stop screw? The rpm should stay the same and IAC should do the opposite of how you turn the idle stop screw until you run out of IAC steps. For example, if you back the screw out to close the throttle blades then the IAC should open to maintain the idle rpm. Try it, close the throttle blades and bring the IAC counts up to into the 40-60 range and see if the idle is still too high.

**EagleMark** · 10-20-2014

If the IAC count is 12 when vehicle is totally warmed up after a highway drive while stopped in drive? Perfect! Litte higher IAC count when neutral...

If idle is higher/lower RPM then desired? Change it in chip.

**lionelhutz** · 10-20-2014

But in neutral with no engine load wouldn't the rpm rise unless the IAC motor closed more, not opened more???

At any rate, I would try closing the throttle blades more and see what happens.