When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I'm looking for some advice on IAC settings and tuning for idle. I've read a lot of threads and made some changes with really no changes. In all honesty I'm not really sure I've understood everything I've read or tried. This tuning is all brand new to me.
I'm running a 383 with LPE219 Cam and AFR 190 heads. She runs good but not perfect especially on an initial start. It'll start then bounce between 300 and 900 rpms sometimes stalling. Once I've tried a few times and coerced it with the gas pedal it'll idle fine. Warm idle in gear is fine and steady.
During the warm up process my IAC steps will normally go up to about 144. Right about the time she goes into closed loop they will steadily march down through the 20-50 range right down to 0. I have tried my best to make adjustments to the screw on the TB watching the steps on the EBL screen and they really either seem to climb or drop to 0. I cannot get them to hang in the 20-50 range. (TB is a 58mm Lingenfelter TB if that matters)
This lead me to check for a vacuum leak so I put a vacuum gauge on it and it holds 18 pounds with absolutely zero fluctuation.
Like I said, I am completely new to this so I am probably gonna have to search most of what you guys suggest just to understand but I have to start somewhere I guess.
I'm more of a MAP guy, but my guess is even with a MAF car you're going to need to really tweak the fueling and spark timing for that setup.
Have you already adjusted the bin for your injectors and displacement?
Yes, that is all adjusted. Also, my screen name is misleading. Kept this one for its age and post count but the car is actually a ‘92 Z28 so it is a MAP car
I'm looking for some advice on IAC settings and tuning for idle. I've read a lot of threads and made some changes with really no changes. In all honesty I'm not really sure I've understood everything I've read or tried. This tuning is all brand new to me.
You have to indicate which Bin you started with, and what sized injectors you are running. Be sure to confirm your Base timing by hand matches your Initial timing in the Bin as its' reference, and make sure you have the correct engine size and injector flow. Since the injectors are more than likely larger than stock you would need to adjust a few fueling areas ahead of time to compensate for that difference to try to get the fueling as close as you can before even getting started. You want it as close as possible without O2 correction, this will guarantee the smoothest idle possible with O2 correction. A modded engine will also need its' idle RPM raised a tad as well, a cammed 383 will not like 600-RPM at idle, but there is no datalog to confirm most of that. The IAC reading 0 (closed) is telling you the engine is getting its' air from another source. You confirmed that you do not have a vacuum leak, so it has to be the throttle body. It's opened too much at idle...
Close the throttle body all the way with your torx or screwdriver, and see if your steps go up to where they need to be. Keep the throttle body closed and wait for the IAC to adjust and settle itself somewhere, and that needs to be done at operating temperature. You can tweak the throttle blades open or closed here and there until you are happy with the idle steps, but you have to give it some time to move and settle itself. Once that is done, set your TPS percentage. You're running an aftermarket throttle body, so the TPS idle percentage will probably be off. If the sensor is adjustable, you can set it by hand the way you did when you installed the larger throttle body, just loosen it, and move it to the proper percentage at idle and retighten it. If it is not adjustable, then you can adjust its' off idle percentage in the Bin to help compensate. It's not difficult to do, but believe me... I understand that when you're new to it it can get frustrating.
You have to indicate which Bin you started with, and what sized injectors you are running. Be sure to confirm your Base timing by hand matches your Initial timing in the Bin as its' reference, and make sure you have the correct engine size and injector flow. Since the injectors are more than likely larger than stock you would need to adjust a few fueling areas ahead of time to compensate for that difference to try to get the fueling as close as you can before even getting started. You want it as close as possible without O2 correction, this will guarantee the smoothest idle possible with O2 correction. A modded engine will also need its' idle RPM raised a tad as well, a cammed 383 will not like 600-RPM at idle, but there is no datalog to confirm most of that. The IAC reading 0 (closed) is telling you the engine is getting its' air from another source. You confirmed that you do not have a vacuum leak, so it has to be the throttle body. It's opened too much at idle...
Close the throttle body all the way with your torx or screwdriver, and see if your steps go up to where they need to be. Keep the throttle body closed and wait for the IAC to adjust and settle itself somewhere, and that needs to be done at operating temperature. You can tweak the throttle blades open or closed here and there until you are happy with the idle steps, but you have to give it some time to move and settle itself. Once that is done, set your TPS percentage. You're running an aftermarket throttle body, so the TPS idle percentage will probably be off. If the sensor is adjustable, you can set it by hand the way you did when you installed the larger throttle body, just loosen it, and move it to the proper percentage at idle and retighten it. If it is not adjustable, then you can adjust its' off idle percentage in the Bin to help compensate. It's not difficult to do, but believe me... I understand that when you're new to it it can get frustrating.
Attach your Bin file.
- Rob
I think I started with the 350 aluminum head bin and set it for my displacement and 36lb/hr injectors that I have. My heads are AFR Vortec but I haven't seen anything Vortec specific in all the reading I've done so I don't think I have to set anything for that.
My initial SA is set at 8, which matches the mechanical setting.
I see you started doing VE Learns off of 3006, but try to smooth it out now. It's pulling fuel during the Learn, so find the lowest point during your Learns that now read 0% during the Learn, then smooth out the surrounding idle area...
The vacuum leak would allow the engine to draw in the idle air it needs from location(s) besides the IAC, which would cause the ECM to close the IAC in order to get the engine to idle down.
It may not register as a loss of vacuum on a gauge.
I added the injector data. I swear I had it in there before but I guess not. Cold starts are a good deal better but it does bounce 100 or 200 RPMs for a little bit.
I’m going to have to smoke my intake because I cannot get the IAC count perfect. At least it matches up/down VERY slowly but I cannot get it to stay in 20-50 range. I can get it to maintain within the 70-90 range while driving but not idling.
One thing Im noticing is I am getting some high knock counts but I don’t hear any. Not sure if I would though with 11:1 compression and the GMMG exhaust lol. Im leaving open the possibility of false knock for now because I do have an exhaust rattle I have to figure out.
Im going to do a couple more VE learns with the injector numbers corrected and maybe this weekend smoke the intake and see where I am at.
my luck I will get nowhere and be back bugging you guys. Thanks.
Do you have the OEM 48mm throttle body? Wonder if the aftermarket 58 could be causing problems. I tried a BBK 58mm once and the throttle blade to bore fit tolerances were pretty $h!tty. I couldn't get the damn thing to idle down due to how much air was getting past the closed throttle blades. Ended up going back to my current SLP 52mm that's been going strong since 1995.
You're running 11:1? Wow... On what octane fuel? I know larger overlap cams can bleed off some dynamic compression making higher static compressions more streetable, but I'm not sure that LPE cam would be sufficient to facilitate 11:1 on pump gas??
Yeah, getting the right injector offset voltages into the calibration are critical with injector swaps.
In the factory $8D code there is an spark timing vs idle speed error parameter that will change the spark timing when the idle RPM fluctuates past a certain amount... factory settings allow the ECM to add or subtract 5° based on whether the idle speed goes higher or lower than the prescribed idle speed. This can sometimes cause a bouncy idle on modified engines, so we sometimes advise to zero those tables out. Not sure if the EBL has the same thing.
I do have a 48 still. I'll look into that if a smoke test doesn't show anything.
Yeah 11:1. Possibly even a tad higher. Running 93.
I'll look into those parameters you mentioned. Its wierd because its only on startup idle and a little bit after. Once driving idle is rock steady.
I do have another question. My last run after a VE learn it seemed like coming to a stop to RPM's wanted to dip a little too low for a split second. I'm guessing the previous VE learn pulled a little too much fuel from my idle rpms. This current learn (pictured below) looks to want to pull more fuel form the area below where I idle. I idle at about 900. Should I not apply this learn?
I have a hunch your knocking is real... running over 11:1 even on 93 seems like too much IMO with cam that's somewhat mild for a 383.
If the EBL has a decel enlean subroutine, may want to look at that if you're getting momentary RPM drops coming to a stop... or IAC throttle follower subroutine. These are things I would do if I was looking at $8D... but again, I don't know how the EBL is setup.
I have a hunch your knocking is real... running over 11:1 even on 93 seems like too much IMO with cam that's somewhat mild for a 383.
If the EBL has a decel enlean subroutine, may want to look at that if you're getting momentary RPM drops coming to a stop... or IAC throttle follower subroutine. These are things I would do if I was looking at $8D... but again, I don't know how the EBL is setup.
It may very well be real. Probably is, I think it’s only happening after a long hot idle. I don’t think my rad is up to the task. Good enough for now but next season I will probably upgrade that. I have a 160 tstat and when moving keeps it around 185ish but idling she’ll get up to 235.
Any thoughts on that VE learn pictured above pulling fuel below idle rpms
also, thanks for all your help. I really need this.
VE learn (I'm assuming from the 8D stock tables) seems like it makes sense..
If I'm thinking about this correctly... at idle rpm, your cam has A LOT more overlap than the stock cam... stock cams had ridiculously wide LSA's. So you're throwing more unburnt oxygen out the exhaust which the ECM will interpret as running lean. So I guess I would have expected to see the VE learn put in more fuel, not reduce it? Maybe RBob or one of other more knowledgable folks can sanity check me on that...
At above idle and into the 2000 rpm range, I guess I'd expect less fuel since the SuperRam probably doesn't have the same volumetric efficiency as a full runner TPI?
I put my smoke machine on it yesterday and THANK GOD the SuperRam did not have any leaks. Anyone with a SuperRam or worked on one will understand that relief. I did have a leak where the vapor canister line goes into the throttle body. I got that fixed. Also had slight smoke coming around the throttle body blades and also where little arm comes through to the TPS. They were very light though so I am hoping its less than the "minimum air" amount and I can work with it.
Also realized I am in idiot and I have been trying to set IAC steps in idle so that seems to have been my problem. Looks like I have it adjusted to the mid 20's now with it in gear. Moves around a little up and down but looks like I'll call it 24.
Only thing I am noticing now is my BLM is at 108 and INT 126/128. I haven't driven or completed any learns since fixing vacuum leak and adjusting the IAC and that is all that has changed so we shall see when this threat of storms passes.
I've gotten the car in a lot better tune so far. But the idle on a fresh start is really starting to bug me. I'm hoping someone will please look at my datalog and Bin and let me know if you see something. I know I am new to this but I can't seem to figure anything out. On a fresh start the RPM's will bounces from 400ish to 700ish a few times then it will stall. On restart it will need pedal to start and do the same thing. Once I put the slightest pressure on the pedal to smooth it out (slight enough it doesn't even register TPS%) for a little bit. Less than a minute. It will get much better and bounce slightly on its own without stalling. Then after about a minute it will go into closed look and idle rock steady and start up fine for following start ups.
Any ideas what I should be looking at?
The first idle bounce data log is the start up attempts
the second one is after its gone into closed loop and idles great, I should have just let it keep logging but didn't so its split into 2
I was wondering if the transmission is a stick or auto. I don't see the TCC flag set, but the WUD is showing P/N being active.
With the idle speed you are requesting, should increase this value to 1200 RPM:
BLM - Idle Cell RPM Threshold
There are two issues at idle, too much IAC is required and the BLM drops to 108 (removing a lot of fuel). Open the throttle blades some to get the IAC closed down. This is likely what is causing the bouncing /stalling cold idle.
It would likely be helpful to increase the idle SA parameter. Try it at 24° BTDC.
The TPS percentage looks off, look at the Diagnostic Screen, it's at 0.9 with maxed out steps. You need to loosen your TPS sensor and open the throttle body so the engine can breath. Like Bob said, get your IAC steps down by opening the throttle blades (between 25 to 30 steps at warm operating idle, not at 0), then position your TPS sensor to read 0.5% on the Diagnostic Screen then tighten it. Thought I mentioned that earlier bout the IAC and TPS at operating temp...
I was wondering if the transmission is a stick or auto. I don't see the TCC flag set, but the WUD is showing P/N being active.
With the idle speed you are requesting, should increase this value to 1200 RPM:
BLM - Idle Cell RPM Threshold
There are two issues at idle, too much IAC is required and the BLM drops to 108 (removing a lot of fuel). Open the throttle blades some to get the IAC closed down. This is likely what is causing the bouncing /stalling cold idle.
It would likely be helpful to increase the idle SA parameter. Try it at 24° BTDC.
RBob.
It is auto that was a setting I forgot to go back to. Originally choose 3006 which is 6 speed because it listed aluminum heads.
I am having trouble finding the "BLM - Idle Cell RPM Threshold" I even used the search and cannot find it.
The way I am reading the advice from you and street lethal seems contradictory to what I am seeing. Your saying open the throttle up but to set my IAC it says to be at operating temperature and in gear. I have it set to achieve the 20/30 steps at temp in gear but then that gives me those high numbers in the datalog above on a fresh start
I fixed the injector offset. Somehow I guess I grabbed a wrong version to play with. That is back where it should be for my injectors. I also adjusted the TPS. It ow reads 1% since that is the minimum it displays.
Now its warmed up so I cant tell if these changes make a difference on a fresh start.
I would like to find the BLM idle threshold youre talking about though.
The way I am reading the advice from you and street lethal seems contradictory to what I am seeing...
Your BLM is pegged rich in Closed Loop w/O2 correction, you are maintaining idle with 145 IAC steps (fully open) at close to operating temperature in Closed Loop, it's choking. You are surging in Open Loop without O2 correction with a predetermined fueling where fuel is meant to be more due to the increased air density. Your throttle blades are closed too much for your engine kPa, open your throttle blades so the engine can breath. The IAC is meant to control idle air at 25-35 steps at operating temperature, then extend to 145 steps at wide open throttle (fully extended TPS), that's its' proper range. Your TPS% is off. You need to open your throttle blades to bring the IAC steps down to 25-35 steps at operating temperature, and bring your TPS% to 0.5...
Your BLM is pegged rich in Closed Loop w/O2 correction, you are maintaining idle with 145 IAC steps (fully open) at close to operating temperature in Closed Loop, it's choking. You are surging in Open Loop without O2 correction with a predetermined fueling where fuel is meant to be more due to the increased air density. Your throttle blades are closed too much for your engine kPa, open your throttle blades so the engine can breath. The IAC is meant to control idle air at 25-35 steps at operating temperature, then extend to 145 steps at wide open throttle (fully extended TPS), that's its' proper range. Your TPS% is off. You need to open your throttle blades to bring the IAC steps down to 25-35 steps at operating temperature, and bring your TPS% to 0.5...
- Rob
When I turn the screw in and open them up the ic steps go to zero and it raises my idle. Am I doing something wrong here? Feel like an idiot and that’s a basic instruction but I don’t seem to be getting the results described.
also where would I be able to see half percents? The main display shows only while numbers. In the diagnostic screen it just shows volts. Or should I just figure out what .5% is in volts.
Sometimes the TPS sensor, depending on if it was replaced or not, can be off. It's no big deal. You have to wait and give the IAC steps time to adjust, it's not immediate. Just try this; loosen the TPS so that you can barely move it, and lower it from 0.9% on the Diagnostic Screen, to about 0.2%. Then, open the throttle blades (if you have already, then close them again), and wait for the IAC steps to adjust for 25-35 steps on the main WUD screen. This needs to be done at operating temperature, so whatever you're set for (185*F or 200* F), just get the engine to that temperature, then open/close the throttle blades and wait for 30 IAC steps. Zero is too much, that means the IAC is fully closed.. Once it gets to 30 steps (give it time, let it adjust), then leave it alone. Don't touch it anymore. Then toggle to the Diagnostic Screen, move the TPS with your hand until you see 0.5%, then tighten it. Should take you 30/40 seconds to do everything once the engine is fully warmed up.
I think Rob is typo'ing the percent when he means volts on the TPS setting.
RBob.
Yeah, I have a bad habit of typing too fast without proof reading before submitting. You'll sometimes catch me typing IAC as IAT and vice versa quite a few times as well...
Ok, Thought I got somewhere this morning. Maybe I did, maybe not. With the advanced XDF I changed the BLM Idle Threshold to 1200. I warmed it up and tried to adjust my TPS. It would not go lower than .9v. I swapped out to my old TPS, which was still fine and only replaced so all sensors were new with the swap. That I adjusted down to .2V and then adjusted the IAC again. Got that where I liked it, I think 27 it was. Then adjusted the TPS to .5V. Throttle percent was reading like 9% so I restarted the car to zero that out. Checked IAC again and they just kept climbing above 50.
I adjusted it slightly and its mostly in the 30's but if I let it go long enough it eventually does a slow march up 50+.
I smoke tested this thing for vacuum leaks the other day and have none anywhere except very slightly at the throttle blades (I would assume this could me the minimum air) and also, again very slightly smoke) at where the throttle blade shaft comes through to the TPS sensor.
How slowly should the IAC take to get to its destination and once there should it change much or be rock steady. I think I am going to be throttle body shopping.
I'll have to wait till it cools for a while to see how it starts up.
I don't believe you have a vacuum leak anywhere. Even with the IAC fully extended at idle (as per your last warm datalog) your INT/BLM was 128/110 for the majority of the playback, from 125* F to 138* F. You were rock solid at 49 kPa, which is about 16" of vacuum at idle the whole time. The only problem I see is your IAC is providing most of the engine's air supply at Closed Loop idle which means your engine is choking during warmup, which is why you're not seeing a rock solid 1200-RPM on a cold start. You're surging when cold because the VE is being multiplied during cold start and Open Loop, and it needs more air to help burn the fuel. In Closed Loop it settles and smooth's out because with the IAC being fully extended, the VE is right at the borderline of allowing O2 correction to compensate. 110 BLM is rich, but your INT is maintaining...
If you let me do a Bin for you, I'll pull 8% of fuel out of your VE table which will bring your INT/BLM closer to 128/128 stoich, as well as smooth it out for you. You are not that far from that part. All that's missing are your IAC steps. They fluctuate depending on CTS, which is why I told you that you will want to set them at your final operating temperature. You will see 35 steps at say 190*F, but when the fan kicks in, and brings the CTS down to say 175*, not only will the steps increase due to the cooler temperatures, but there is also a table that compensates for your IAC steps when the fan kicks in, so more steps are added. You will never see a constant 30 steps, you want them to average that at your operating temperature and with the fans off...
Look at a screenshot of your datalog. Your IAC is programmed to be fully extended at 145 steps, but during the datalog between 125* F and 138* F (not even fully warmed up yet), it was going back and forth from 145 steps, to 144 steps, so it wasn't entirely maxed out at that temperature. Had you allowed the datalog to reach 185* F, you would have seen the IAC steps go down even more, the problem here though is that they are not low enough at these particular temperatures. Key on when cold your IAC steps should be set for 145 steps. Once started when cold, you will see them adjust and go down slightly, and at 100*F, you should be right around the 90 to 100 step mark. At 120* F Closed Loop enables, and the VE is no longer being multiplied, so from 120* F to Operating temperature, the IAC steps should go down from 70 steps or so, down to 30 steps as your final just before your fans kick in. Also note that if your BLM is already reading an extremely rich 109 in Closed Loop idle with O2 correction and with no warmup multiplier, just imagine how rich you are when you're engine is cold at 60* F to 100* F with a fuel multiplier being active, and with only the aid of the IAC steps that are barely keeping the engine alive at 138* F during Closed Loop as it already is...
Rob, yeah if you want to throw a bin together for me I'm not proud, I'd love to see what you can do. I'm attaching my most current one with having changed the BLM idle threshold and doing some learns over the weekend. Also in the zip is a longer datalog from this morning as I was trying to get the IAC correct dialed in.
I just looked at your datalog, I see that you opened the throttle blades, so now the INT/BLM worked itself out because you're letting in the necessary air,not to mention the steps went from pegged to closed. Do you see? I'll attach two pics below. However, now you went too far with the IAC step settings. Instead of it being pegged open, now it's completely closed at times. You have to find that happy medium again, and do it slowly. The TPS voltage is definitely off by a tad, so fix that issue while you're setting the IAC again. Get the engine to operating temperature, loosen the TPS sensor (leave it semi loose, but a tad tight/secure so that it's not flopping around, but that you can move it with your fingers), and slowly close the throttle body blades with the torx. Don't worry about the TPS voltage being close to 0.10 at this point. Close the throttle blades slowly at 195* F, and just wait for those IAC steps to reach 30 to 35 steps from the current 0. Try to do this before the fans kick on, so if the fans are set at 200* F, do the process at 190* F to buy you some time while you wait for the steps to rise. Once you see 30 to 35 steps, stop, leave it alone, then toggle over to the Diagnostic Screen. The TPS will be much lower than 0.50 at this point because you're starting with 0.50 and closing the throttle blades, so it might be closer to 0.20 again, so with you fingers move it back to 0.50 and tighten it. Done. The BLM is close now with the opening of the throttle blades because now it can breath, so you don't need a new Bin, you just need to finalize those IAC steps...
The BLM is close now with the opening of the throttle blades because now it can breath, so you don't need a new Bin, you just need to finalize those IAC steps...
Actually, I'm looking at the Bin your using even deeper now. Yes, the INT/BLM are close in the datalog at idle, but the other areas in the VE as well as everywhere else in the Bin are kinda off, and quite restricting. I will make that 383 pull you like a raped ape if you'd like me too...
Actually, I'm looking at the Bin your using even deeper now. Yes, the INT/BLM are close in the datalog at idle, but the other areas in the VE as well as everywhere else in the Bin are kinda off, and quite restricting. I will make that 383 pull you like a raped ape if you'd like me too...
- Rob
I would love that. This thing can move pretty good now but I know it has a lot more in it. I like to blame it on the 2.73 gears.
I haven’t been able to get it to VE learn upper RPMs because anything over 3,600 RPMs with 2.73s and a 383 is suddenly 80-90-100 mph
Im game for whatever you want to do. I think a 383 SuperRam with cam and heads ad 1.6’s off a fresh install is a bit above my learning curve.
... and increase it from 3600-RPM to 6000-RPM. This will increase your Learn range.
Then go into;
PE - TPS Enable Threshold
PE - MAP Enable Threshold
... and increase all of the values to 99.99 so that it will lock you in Closed Loop so that it will Learn all cells. Once they are Learned, restore the PE values back to where they were..
- Rob
Edit: You're only an hour and a half away from me. It probably takes us both an hour to get to Island Dragway, can tune it right on the track if you'd like. The 2.73's aren't an issue with what I am seeing.
Last edited by Street Lethal; Jun 13, 2021 at 06:39 PM.
