I seem to notice that a number of people, after filling in the IAC opening, are choosing to not re-cut air passages to reroute the needed combustion air, but instead are adjusting the throttle plate opening to compensate for this. Personally, I would not recommend this, especially on someone else's vehicle. The IAC, through feedback from the ECM, helps to regulate the speed of idle under load, such as when the A/C is turned on, or when the trans is shifted into Drive from Park, or when the clutch is engaged slowly at an idle. Up here in Saskatchewan, when in winter, the intake air temperature at start-up may be as low as -30 to -40 F. The idle, assuming that the vehicle has been plugged in, will be a couple of hundred rpm higher (as most vehicles upon cold start-up) without the accelerator being touched and will maintain that for a number of minutes until the ECM senses the conditions as being appropriate to lower the idle to the normal range. This will not happen if one only cracks the throttle opening wider instead of cutting air passages for the IAC valve.

Any other opinions on this?

Thanks.
Luke

I agree Luke,

My experience is that, depending on the computer, most vehicles won't run or start if the IAC is totally plugged. I have not encountered a vehicle yet which I can plug the IAC entirely and get it to run properly. What I've seen happen a number of times is you adjust the plate warm (with a restricted IAC) and when you go to start it up cold it won't even run. That is why the IAC restriction procedure usually takes a number of tweaks at differing conditions to make it right. Restricting the idle air pathway is an advanced process. I've seen benefits when it is done properly but it is very experimental. I recommend that people new to the modification process concentrate on the Groove and PCV vacuum plugging and spark plug gap increasing only, especially if you are doing it for customers. If you start restricting the IAC, you are opening up an experimental project which will end up not being good for business as you risk having unhappy customers who would have been very happy if you would have left their IAC alone.

We need to focus on getting the Grooves cut correctly and the vacuum system integrity correct. That, along with getting accurate pre and post mpg measurements, is quite a bit to manage.

Great discussion point. Anyone want to weigh in on this one?

I am a newbie at all this... ButI have to agree w/ Luke and Nick on this. IAC operation is necessary for different operating conditions, esp. cold startup. Those Grooving vehicles in warm Southern climes might not have had much issue here. But when I grooved the 91 Jeep Cherokee, I thought about reasons for having the IAC operate, and realized I couldn't just block it off. I re-directed and also reduced the amount of airflow in this system and also slightly increased throttle plate opening via the idle stop screw. IT seems to have been OK. But other engines I'm looking at have the IAC motor/valve mounted somewhere not on Throttle body, and messing with that type of downstream IAC path seems tricky/risky to me. Well i've been posting a lot lately, time to get some more Grooving and less talking done!! TracyG