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I've read 50 threads about IAC adjustment and none of them dealt with a constantly moving IAC step number that won't settle anywhere.
First the specs:
66 Chevy C-10
416ci, DBC, 02' Fbody ECU, stock LS3 heads, Holley high ram intake, 102 Holley TB, 42lb/hr injectors, 58psi at the regulator, custom 1 7/8 headers
Cam Motion street grind- 226/236 @.050, 598/598 on a 117lsa
Tremec TKO500 5 speed, ls7 clutch
I went around in circles and finally found I had a sticky throttle blade that would not come to a rest all the way back down on the adjustment screw. Fixed it. Now on the getting the IAC steps in line. I've flashed tunes bringing the steps up and down the IAC Steps vs. Effective Area table and brought the numbers in the cells closer together trying to get dynamic and desired airflow closer together and IAC steps to register and stop somewhere with no luck. I've been reseting the IAC and TPS after every adjustment. There's an 1/8th inch hole in the throttle blade and the TPS voltage is at .60. Any help or suggestions are appreciated.
It'll never completely settle out. It'll be in a range. Say 20-40 hot. With that hole, you probably need to move the whole IAC effective are table over to the right 5 cells or so. I wouldn't mess with the values in the cells themselves. They are pretty good from GM.
If the adjustment is swinging more wildly than that, then you have an issue with fueling and/or spark. The motor is surging and the IAC is trying (and losing) to keep it idling. That cam should be very easy to tune in a 416.
Thanks for the reply! The IAC steps either end up at 0 or the max number on the IAC steps vs. Effective area table. I'll have to go to the tune repository and grab the stock numbers for that table and plug them back in. I'm not sure they were stock from my first tune moving forward, so I can't go back to a previous tune and grab them. The tune and log are attached below. Also, I have the MAF failed, the adaptive tables zeroed out, the PE turned off trying to run the RAF config. LTFT is still active. Should I turn them off for now while I'm trying to get idle, RAF and VE dialed in? Also, should my goal be to match idle desired and dynamic idle air as close as possible? I'm going to double check tomorrow that I don't have a header gasket leak. Thought I heard a little ticking and want to make sure.
Thanks again!
I double checked headers and there isn't a leak. I've been up and down with the BRAF and the IAC vs. Effective scale and I still can't get the IAC counts to stop anywhere. It migrates one way or the other till it's at 0 or completely maxed out. Am I right to think that by getting idle desired and dynamic idle air close to each other that I'll be roughed in? I started there and got them within a couple g/s and then started moving the IAC vs. Effective table one cell at a time and balancing the idle out by opening/closing the blade. I'd go to far to the right and end up at 0, then too far to the left and end up at the max number in the scale. I'm doing TPS relearn every time I turn the screw to get it back to 0. Not sure if I'm missing or overlooking something, but this is getting the best of me so far. There goes another 8 hours.
Went back out and fought it today. Pretty much same scenario except I think I had way too much BRAF and not enough timing, so I roughed them in at 11g/s and 20deg and things smoothed out a bit. IAC still a moving target that never seems to settle. Any suggestions are appreciated.
Well, after a few weeks on and off I had some time today. I decided to take off the Holley 102mm TB and put my old 90mm Nick Williams TB back on. The IAC counts settled at 160 hot. I moved the IAC Steps Vs Effective area values over one place to the right and it fired right up and settled at 30 counts. Smoother idle and faster throttle response too. I guess inexperienced tuner should not start with and engine that has a 102mm TB? What a pain in the ***. Now I can finally move on to RAF tuning and part throttle.
I'm going to make a video on how to correct the IAC effective using the scanner pretty soon. If you still want to try that 102mm later you can try this method. I will say that all idle tuning starts with a spot on VE table. MAF isn't used at idle to determine dynamic air. So putting it in open loop, getting the VE on the money and going from there is a winning method.
Here's the math and PID's you can plug into the user maths:
Idle Desired/Dynamic * IAC position
^^^ That equals the "corrected" IAC step value. Anyway, I'll make a video and show you how to adjust it. It's not hard, just hard to explain.
That is very good on your part. I use excel to build it, because I could never get the scanner to give me throttle effective area as a channel to build the table. Have been using excel but manually realigning it. Never occurred to me to do a math function.
That is very good on your part. I use excel to build it, because I could never get the scanner to give me throttle effective area as a channel to build the table. Have been using excel but manually realigning it. Never occurred to me to do a math function.
I used to use that excel table too, might even be the same one. Then somewhere deeper than a horsec**k in HPT forums I stumbled across that formula. Used it with pretty good success since. Building the table is the fun part, as you have to list the "x" coordinates from 0 to 310 manually, going by at least 5, but on mine I have it down to 2 and even one in the more "popular" areas, like 50 - 100. Haven't had to mess with it since though, seems to work.
Again, that starts with a spot on VE and counts in the 20-50 range with ECT's in the 220-230 range. That's obviously a blade adjustment to get it there, after that it's logging the effective area from a COLD start and adjusting the table, manually. The numbers on the table in the scanner directly correspond with the numbers on the table, but not the column numbers which only go to 120, so you can't exactly copy and paste.
Example:
Table reads 110 and the number above it says 125. I would then find 125 on the table (or whatever is closest) and set it to 110 (or a good estimate using the data), and so forth, just working my way across. It's still pretty manual, but a hell of a lot more accurate.
Here's a pic of my table. Note that the values extend each direction on the x axis from 5 to 320. It's going by "1" in the picture, but on the outer areas where the IAC doesn't get to much (or shouldn't at least unless its cold) are by 3 or so. Also, the scanner won't let you enter 320 numbers in there lol. I tried. So for good data I just make sure to hit the hotspots like 40-100 or so and the rest 3 or 5 intervals.
The filters are TPS less than 0.5 and Dynamic air less than 30 g/s, to allow this to also work while driving.
I know you can easily work with this info Darth, but I'm still gonna do a video on this for the newer guys out there so they can get set this up a little easier lol.
02-08-2019, 08:01 PM
Moving IAC Target, Never Settles 
