MSefi.com read only forum (Jan.15,2018)

Hi all,

I am a newbie to MS, tuning a Porsche 911SC. I am using MSII with an intake from a Carrera 3.2L that has the GM IAC stepper valve installed. The IAC seems to work some days and not others (today, not).

I spent a lot of time yesterday working out the values for the open and close positions, and was then able to tune the Idle Steps curve to keep the idle steady at 1000 through the warm up process. Today it does not work anymore, sometimes the valve stays open when it should have closed, sometimes it does not open on start up. I messed around with the timing variables in TunerStudio (Time Step, Accel Step, Min Steps to Move) with no help - but I don't know what the valve needs. If Time Step is too short the valve won't move at all, but I am not sure if there is a problem with setting it to a higher value than necessary (I would think not, the valve would just move slower). Yesterday I was using a time step of 2.5, Accel step=0, Min Steps=1, temp hysteresis = 5 degrees.

To check operation of the valve, I am starting up TunerStudio with what I think is a good Start (retraction) value and then changing the Crank Steps value to move the valve around. Yesterday the valve seemed to follow the number properly, meaning I could change it over and over, and each time I tabbed out of the field the valve moved to the new position. However, I was mostly moving the valve from full-open to full-closed and not checking the positions in between. (I figured if that worked then the rest could be handled with the Idle Steps curve).

Today I sometimes get the desired high idle at startup, sometimes not. Sometimes the idle sticks at the high idle RPM and drops back way later than the Crank-to-run Taper Time indicates, or not at all.

So I took the valve apart again (and again, and again) to check things out. Each time I adjusted the pintle (by screwing it in or out of the motor body) to get the valve to close at the max step count but the next time I set it to full closed and take it apart again, it is not in the same place.

I spent some time with the valve motor in my hand to see/feel how the pintle moves when I change the Crank Steps value. If I try to close the valve in several steps, by bumping Crank Steps by say 10 each time, the valve moves for the first few changes and then stops moving. It seems to die around 50 steps in. I can jump from 0-100 but if I try to do it in steps it won't move past 50. If I then back it down to 0 the valve will open back up, and then the process repeats. Also, as best I can tell without actually measuring the extension, it sometimes seems to move less than the step change would indicate. For example if I change from 0 to 20 the valve moves x and 20 to 40 the valve moves < x.

Do I have a bad valve, do I need to do the resistor jumper mod on the daughter card, or is there something wrong with the settings that could cause an intermittent problem? I am confused since it worked well yesterday. Prior to that I think it may have been dicey, but there also may have been other problems with the warm up tune (ASE, Warmup Wizard, VE table, etc.) that were screwing things up.

The engine idles nicely at 1000 once warm (if the valve has closed) and if I close the valve and disconnect it, I can get a nice warm up if I feather the throttle, so I think the ASE, Warmup Wizard, and VE entries are in the ballpark.

I plan to try a new valve but if I am way off please let me know.

Thanks,
Scott

The problem seems to be it is inconsistent from day to day. Is the temperature different from day to day when this happens ? I will assume not since you have had it happen often enough to notice if there were a correlation. So all I can think to try are the following:

Set the min steps to move to 5 - that should be enough, but not too much to mess up resolution.

Set the temperature hysteresis to 1 or 0 if it will let you. Hysteresis keeps the motor from constantly moving every time there is some tiny change in temperature. This can be increased a bit once you get it working right. This will also allow you to see step changes sooner, which is important while you are troubleshooting.

Realize that the motor by design only moves every 4 secs, so it may make a partial move then wait 4-5 secs then finish, so be patient after you change a step and give it a chance to react.

Set the time step to whatever allows the motor to move smoothly and consistently over its full range and leave it there. This is the frequency of the move steps put out by the processor and all it affects is how smoothly the motor runs. There is no magic number - it depends on the motor and the load it has to move.

Lastly read and understand the options in the megamanual and make sure you have them configured correctly. For example the extended idle time - you don't need that if the car doesn't need a high idle after it hits normal operating temp, and most cars don't unless they use very thick oil or have a huge cast iron engine that takes forever to warm up the oil.