My IAC a dud?
02-14-2017, 01:54 PM
#1
My IAC a dud? I've been running an AutoZone special IAC for a while, and my airflow is always out of whack on my NW 102 TB. It works. I can command 20 counts or 100 counts and the engine idles differently. So the IAC is moving. But is it moving enough?
The issue is, even when I command 120 counts, I idle at 1000. And I normally idle at 850 with about 30 counts hot. It seems to me that increasing the IAC counts that much should be a much larger increase. With a stock TB, 120 counts puts idle over 1500. I know the NW has a slightly smaller IAC passage, but not that much.
The question came up while my tuner and I were discussing how much Throttle Cracker we are having to give the car to keep it from undershooting idle on return. And the numbers are crazy... like 5X multiplier on 1.5g airflow type deals to push the IAC up close to 100 or over. The car shouldn't require 8-10g more airflow than sitting idle for a clean return to idle. I don't have a supercharger or brick for a flexplate sitting on the crank.
So the question is this: without buying another IAC valve, can I measure if it's actually moving 10 steps if I command it in HPT? Like, how much is that supposed to move? I have a hunch I may command 10 and it moves like 2-3 steps. That makes tuning the IAC effective area and things like Follower and Cracker impossible. Since the PCM commands what it thinks is 2g/sec and the IAC responds by moving the equivalent of .2g/sec.
Otherwise, I may just grab and ACDelco replacement. But I've found non-original electronics to be very hit or miss on this. I went through 5 TPS sensors before going back to the original GM 145k mile unit. It's the only one that worked right. And I had two ACDelco units that were garbage.
The issue is, even when I command 120 counts, I idle at 1000. And I normally idle at 850 with about 30 counts hot. It seems to me that increasing the IAC counts that much should be a much larger increase. With a stock TB, 120 counts puts idle over 1500. I know the NW has a slightly smaller IAC passage, but not that much.
The question came up while my tuner and I were discussing how much Throttle Cracker we are having to give the car to keep it from undershooting idle on return. And the numbers are crazy... like 5X multiplier on 1.5g airflow type deals to push the IAC up close to 100 or over. The car shouldn't require 8-10g more airflow than sitting idle for a clean return to idle. I don't have a supercharger or brick for a flexplate sitting on the crank.
So the question is this: without buying another IAC valve, can I measure if it's actually moving 10 steps if I command it in HPT? Like, how much is that supposed to move? I have a hunch I may command 10 and it moves like 2-3 steps. That makes tuning the IAC effective area and things like Follower and Cracker impossible. Since the PCM commands what it thinks is 2g/sec and the IAC responds by moving the equivalent of .2g/sec.
Otherwise, I may just grab and ACDelco replacement. But I've found non-original electronics to be very hit or miss on this. I went through 5 TPS sensors before going back to the original GM 145k mile unit. It's the only one that worked right. And I had two ACDelco units that were garbage.
02-14-2017, 04:34 PM
#2
Totally the IAC. Replaced with a CarQuest/BWD IAC and now when I set the IAC to 120 it goes to 1600 RPM. As it should.
Now I have to back off my Follower tables as they are for 100 IAC counts when coming to a stop. We wanted it around 60. Now I think 60 would be close.
Now I have to back off my Follower tables as they are for 100 IAC counts when coming to a stop. We wanted it around 60. Now I think 60 would be close.