Surging idle when coasting

[Doc]

Sorry, forgot to ask, stock TB? The key part of your last comment, "adjusted throttle stop down to .5v" This does not make sense to me. When you move the screw the voltage IS going to change. TPS reset, or relearn or whatever, IS the process where the pcm gets it's NEW electro-mechanical "ZERO."

Try this, physically remove the TPS sensor from the TB. With KOEO, observe the TPS voltage while cycling the TPS with your finger 0-100% Your TPS should have a spring inside that helps pull back the wiper to zero position. An old or worn out spring or the plastic not fitting snug enough on the shaft of the TB will produce the phenom of an inconsistent zero. If zero position displays ~+/- .6v don't worry about it.

Bear in mind, the first time pwr/grnd & KOEO the pcm will "record/remember" the physical/mechanical position of the TB shaft as it will produce the voltage output of the TPS sensor displayed on your scan tool.

Sometimes the TPS reset procedure can be a PITA. That is forcing a failure of the TPS.

Big picture, increasing the position of the set screw will (or drilling the TB, not my favorite in 2019) will provide more bypass air to achieve your target idle. The pcm will not "need," the IAC counts. The IAC counts will go down on their own.

2019
Holley LS Throttle Bodies 112-581

A little late to the party but, Holley had some really great ideas with these TBs. Notice the adj bypass air screw on the pass side? You can turn that sucker as much as you want, no TPS reset. On the driver's side, the TPS position is adjustable, so you can get your electrical zero nailed down as well. The adj TPS is really handy on big cam / heads. These TBs are not cheap but, they make things a lot more fun. There are two styles. I would recommend the tapered lip for a street car. The hogged out to the max non lip, I would use on a track only car where you want / need max airflow and don't care about street manners.

[statesman]

yes, drilled a .25" hole and adjusted throttle stop down to .5v when close. Also did a tps relearn.

I tried the RAFPN process to try and adjust the air flow at idle but for some reason it didn't work and showed a constant the entire time.

I adjusted the IAC step table down a few rows like suggested but IAC steps are still around 140ish.

Okay, i think your engine is getting a lot of air. I just looked at your last screenshot and your spark is really low... it shows an average of 12.1 where it should be averaging 20-24. Are you commanding low spark or is it just doing this by itself?

[gpr]

Okay, i think your engine is getting a lot of air. I just looked at your last screenshot and your spark is really low... it shows an average of 12.1 where it should be averaging 20-24. Are you commanding low spark or is it just doing this by itself?

I'm commanding 18 degrees. I tired the RAFPN method but it didn't work and showed a constant the entire time.

Here is my issue. I know i need to adjust the airflow at idle to lower it. However there is a couple ways i can do that.
1. Should I keep playing with the B4403 IAC Effective area table to increase the amount of air flow it is getting per step? This seems to me like a bad idea because the amount of air flow per step should be the same no matter what size hole is in the throttle body blade. (I'm not changing the IAC in anyway so it won't flow more per step)

2. Simply reduce the Desired Airflow at idle because the bigger hole is letting more air in, thus i don't need to require the PCM to allow as much in. By doing this I assume it will close down the IAC steps. Then simply dial in the VE table to get the correct AFR.

Am i on the right track or is there a better method I should be trying?

[Highlander]

Your timing is also too high and your air going in the engine too low...

[gpr]

Ok its been a week but I finally got some time to mess with it. I adjusted the throttle stop out and it is now reading only .5v when close. I also drilled a .25" hole in the throttle body. This seemed to make it run lean so I added 10% fuel to the VE and VE while cranking tables to help it start quicker etc.. as a quick test. Anyway I noticed that the LTFT are showing negative by a lot (probably cause I changed the ve table) but for some reason it is running lean at idle, around 15.5:1. Which i don't know why it would run that lean seemed like before it was always idling around 14.5:1, so not sure why it would pull fuel to make it run leaner.

Also the IAC steps are still around 140 even after the engine is warmed up and idling.

Attached is the log and a screen shot of the log.

Highlander, could you explain a bit more. How is the air going to the engine too low and timing too high? what should they be?

Also I noticed now the map sensor is reading about 8.3 psi now instead of 8.7 psi what it was before I drilled the larger hole.

[statesman]

Also the IAC steps are still around 140 even after the engine is warmed up and idling.

Attached is the log and a screen shot of the log.

I'm on a really tight internet downloads budget right now (metered internet in Australia) so I can't download the latest version of Efilive... which means I can't look at your tune file. The screenshot of your log shows me that your idle airflow is now way too high... When you alter your airflow (cracking the blade or drilling a hole), you need to adjust the IAC Effective area table. I would recommend you shift everything in that table down about 4 or 5 cells and see how close that gets you. The really high idle airflow is what's messing up your idle trims... it's complicated, but trust me on that one. Once you get your airflow sorted out, your trims will fix themselves up and you'll probably have to adjust your VE table again.

[Highlander]

Look at your timing when coasting vs the timing when you are idling... your coasting timing should be slightly lower than the idle timing and the air going through it should be higher than idle. The purpose is to create enough torque reserve so idle routines can easily bring it back to idle.

With all idle routines shut off (no iac adjustments and no timing adjustments) you want your car to naturally idle 200 rpms higher than your commanded, and then let your idle routines bring it down. The more unstable the idle is, (more reversion caused by overlap) the more torque reserve you need to achieve proper deceleration/coming back to idle and idle stability. This is contrary to what most people recommend which they want you to adjust your timing so that you get the most vacuum, thus removing ALL torque reserve from the routine and thus extremely unstable because now no timing changes make any difference in the torque output of the motor that is idling.

[gpr]

Look at your timing when coasting vs the timing when you are idling... your coasting timing should be slightly lower than the idle timing and the air going through it should be higher than idle. The purpose is to create enough torque reserve so idle routines can easily bring it back to idle.

With all idle routines shut off (no iac adjustments and no timing adjustments) you want your car to naturally idle 200 rpms higher than your commanded, and then let your idle routines bring it down. The more unstable the idle is, (more reversion caused by overlap) the more torque reserve you need to achieve proper deceleration/coming back to idle and idle stability. This is contrary to what most people recommend which they want you to adjust your timing so that you get the most vacuum, thus removing ALL torque reserve from the routine and thus extremely unstable because now no timing changes make any difference in the torque output of the motor that is idling.

I'm a little confused by this. How is it even possible to get your spark timing when coasting less then when your at idle? Because when I'm going down the highway and let off timing usually goes to 40 which is what is commanded in my High octane spark table, then as I slow down and the engine rpms come down it drops back to 18 which is what is also commanded in High Octane Spark.

Or are you talking about if I am in park and rev the engine and let it come back down on its own? As the rpms come down the spark should be less then when it is trying to maintain idle? Because in the last log I posted and on the screen shot shows where I cracked the throttle. You can see the engine rev and as it comes back down it goes to the default 18 degrees and stays there for about 5 seconds before it starts changing. It looks like where the timing is at 18 degrees the rpms are too high. This leads me to believe i am commanding to much air flow or it is getting too much from the larger throttle blade hole.

Also why does it take so long before it starts to correct the idle by changing the timing? The vehicle isn't moving and the throttle % is .4% like it should be.

[statesman]

How is it even possible to get your spark timing when coasting less then when your at idle?

Is this a serious question?

Because when I'm going down the highway and let off timing usually goes to 40 which is what is commanded in my High octane spark table,

Oh look, you've already answered your own question.

[Highlander]

Also.. check your intake are temp sensor.. Why is it -38? this causes huge problems with VE calculations and other idle adjustments. Car needs to be 100% before touching the computer. Your trims are way too negative, which means the vehicle is overfueled and the STFTs are catching up. During those issues you will have a lot of instability. FIX THOSE FIRST.