High idle on cold start: vacuum leak or IAC setup?

[FABombjoy]

I also noticed that the car wants to stall if I quickly take my foot off the accelerator. I tried adding more fuel to the leftmost column of the VE table, but it didn't help as much as I thought it might.

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[jangell]

I took a log, but forgot to bring home my laptop yesterday. I’ll be sure to bring it back today and get the log off it.

— Joe

[opethmike]

Did you know that if you make out with the car, that it will LS swap it self?

[jangell]

Here's the log and tune. This includes a couple of stalls and revving at idle before driving around the block on auto-tune. I was tinkering a bit with the leftmost VE table cells while idling, and auto-tune messed with the rest of the table while driving, and thus the tune is from after all that tinkering/auto-tuning.

CurrentTune.msq
2018-12-24_14.28.18.msl

There's a lip at the edge of my garage. I have to give it more power to get over the lip, then release the gas as soon as I'm actually over it so I don't rush into traffic. That's how I was able to trigger the deceleration stalls so easily.

My uninformed guess about what to do next would be to slightly increase the timing on the leftmost cells? Since I've already upped the fuel in the leftmost VE cells, that seems like the next thing to try.

Thanks!

-- Joe

[FABombjoy]

Based on my experiences, building a wall against stalling should be done using spark advance. The VE table will probably only have a minimal effect and will probably cause warmup fuel to be excessive.

A few immediate thoughts:
-Where is TPS? I know that TPS is critical in MS3 for accuracy of idle control, but it doesn't look to be quite as used in MS2. I didn't see a concept of "engine states" in your tune, so TPS may only be useful for accel enrich and such.
-Revert the VE and bring idle AFRs back into the 14.x range
-Open up your base idle screws a bit. When you have a stable warm idle, MS opens the IAC valve to 6-7 steps. See if you can get that to almost 0.

Your spark table has 5 duplicated columns: 3100 through 6000 are almost the same. There are some shenanigans going on in 3100 but we'll pretend that's a keyboarding error. This means you could rescale the table and add some low-RPM resolution.

Your low RPM breakpoints are 500, 950, and 1200 but the target RPM is 790. This means you're always going be at an interpolated spark advance value, making it challenging to fine tune those columns. The high advance values in 1200 are causing frequent, consistent oscillation when you transition from on- to off-throttle.

I would shift the advance table around to free up some low-end advance columns. Then set your 500 RPM column to +1 or +2 degrees as an anti-stall measure. Put your VE back to where it was so that you don't have a big rich idle and you should have much better off-throttle driving response.

[jangell]

TPS: I do have a TPS, which is located on the Mustang throttle body opposite the throttle cables (the body is designed for one). I’m having a problem where whenever I snug the TPS bolts down, the it no longer turns with the throttle. I’ve gone through three of these over the years of testing as this binding evenrually ruins them. I’m worried that if I make it too loose that I’ll have a vacuum leak. I’m going to try making a thicker gasket to space it a bit more and see if that fixes the binding.

From what I can tell MS 2 mostly uses the TPS for more responsive acceleration enrichment, so it’s optional in my setup, but it would be nice if it worked. I don’t recall seeing anything about “engine states” mentioned anywhere before, but I know MS 3 has some more advanced stuff, and I mostly just didn’t read anything MS 3 specific so I wouldn’t be tempted to upgrade.

VE: will do. I had a feeling that the leftmost VE column wasn’t doing much to prevent decel stalling.

Base Idle Screw: ok. I had been planning to let the IAC completely control idle, and just close the throttle all the way, but it seems that I need to crack the throttle to get the idle up above 650. My theory was that this was the first tim is out the air filter on, and now it can’t suck enough air through just the IAC, but That doesn’t seem right. Without the air filter, it seemed to be able to idle around 790 just fine with the throttle completely closed, and with the IAC open all the way would rev to 2000, so I didn’t think I was losing any useful headroom by letting the IAC manage with a closed throttle. Of course, I haven’t actually tuned the warmup yet (I was going to let warm up auto-tune handle that, which is more likely the reason I needed to crack the throttle when the air filter was on (I literally just realized this; it makes a lot more sense than my other theory).

Anyway, I’m fine with the IAC being zero at idle to. I was watching the RPMs more than the IAC steps, so I’ll monitor that on next start.

Spark table: that’s almost completely auto-generated. I have no idea how to adjust it at all. The only cells I changed are a 2x3 block around my idle, which I set to 14.

I set the low columns to 500 and 900 but put 14 in adjacent idle cells in the theory that it would just interpolate to 14 at 790 RPM. As opposed to setting the second column to 790, as that would cause interpolation in a 3x3 grid. Or at least that’s how I understood it.

I’m good with adding more low RPM columns. I’m just not really sure how important the high ROM columns are or what values I need in those columns when I reassign. Since you noted that I have duplicate columns, can I safely just reassign the the lower columns fornidle ranges, and just interpolate the higher columns?

Thanks!

— Joe

[FABombjoy]

Base Idle Screw: ok. I had been planning to let the IAC completely control idle, and just close the throttle all the way, but it seems that I need to crack the throttle to get the idle up above 650.

You can also set the IAC minimum steps, but then you might cheat yourself out of the max ability of the IAC to control RPM under all conditions.

Spark table: that’s almost completely auto-generated. I have no idea how to adjust it at all. The only cells I changed are a 2x3 block around my idle, which I set to 14.

https://www.youtube.com/watch?v=CiqrSJIITGY

I’m good with adding more low RPM columns. I’m just not really sure how important the high ROM columns are or what values I need in those columns when I reassign. Since you noted that I have duplicate columns, can I safely just reassign the the lower columns fornidle ranges, and just interpolate the higher columns?

Exactly! The above video shows how to rescale with interpolate, which will help you shift everything over and make room for some fine-tuning in the idle ranges.

[jangell]

Thanks for the video -- I had seen that button in the some post months ago, and completely forgotten about it. It's one of those "complete visible but well hidden" bits of UI. I had no problem using that to add more columns.

I set up the new ignition table and VE table, adding leftmost columns for better idle control. It seems to idle fine (+/- 30 RPM), but I'm still having problems with stalling when I quickly take my foot off the throttle (ie: foot down and up fast, causing it to rev then go back to idle, but it drops down low and stalls). I boosted the low column of the ignition table to 17+ degrees, and tried as high as 25 degrees at one point, but it didn't seem to help. Not sure what I'm missing here. Not sure how much it matters, but the throttle screw is only slightly cracked. Idle motor steps are close to 0 (seems to be around 6 sometimes, but usually 0).

The TPS is still no good. It seems to work sometimes, and not at other times. I finally looked at it more closely, and the part number seems to be a Dodge/Chrysler unit that is MOSTLY the same as the Ford TPS that the Mustang throttle body expects, but not exactly. For example, the "ears" that grab the throttle bar thing are smaller in the Dodge, and the diameter of the barrel is a little different, which may be what's causing all the binding. Of course, a Mustang TPS has an upward-pointing connector, which interferes with the plumbing for the air duct, and there isn't enough clearance to point it downwards instead. Still, I might hit a junkyard tomorrow morning and source one just to try it out, and see if I can come up with a way to route around the air intake.

Other than that, I flushed and filled the brake system, so if I can get this stalling stuff figured out I should be able to take it for another drive. It starts pretty readily, so if I did stall at a stop sign or something I could restart it easily enough, but since I'll need to get the stalling resolved at some point I might as well do that now.

A couple of logs and the tune are attached. The longest log includes some auto-tuning, which I reverted while I tried to get the revving figured out. The shorter log contains contains a clean VE table and the new ignition table.

Thanks!

-- Joe

2018-12-29_13.12.36.msl
2018-12-29_12.42.12.msl
CurrentTune.msq

[Bitsyncmaster]

I set that curb idle screw by turning it in on a hot idling engine until the closed loop idle can not comenate any more (idle goes higher RPM). Then I back off that screw about 1/8 or 1/4 turn. That should help your stalling problem when you take your foot off the gas quickly.

That's with the stock K-jet but it may help you the same.

[jangell]

Thanks -- I'll check that tomorrow. I'm trying to get it so that the IAC steps are close to 0 when warmed up, which would mean that the IAC is completely closed and that the lowest RPM at idle is held by the throttle screw alone. But it seemed like it only needed a very slight turn to do that -- I think a half turn, but I don't recall exactly.

I did notice that once the engine was in gear, it dropped to the 650-700 range -- I only just remembered that because I spent most of my time tinkering with the car in Park. Maybe I should target closer to 850-900 for an idle, and keep the idle screw a bit more open, then see if it drops back to 790 or so when in gear. I'll have to check again tomorrow and see what it's doing, as it's likely I'm remembering this all wrong right now.

-- Joe