Hello,

As some of you may know, I recently finished a build with my 427 and even had it dyno tuned for WoT. (The tuner was horrible, this is a long story, w/e). The tuner didn't tune anything below WoT, so I took it upon myself to tune the car via HPtuner MPVI2.
I've got the tuning down, everything is smooth (tuning via Wide Band + Street tune). However I'm running in to an issue:

'99 Trans Am
427 Swap
Manual, T56

From a cold start, I let it warm up to operating temperatures at idle (170 to 185ish). But when I get in to the throttle a little and then let off, the RPM's drop to 350-400 range. It takes forever to recover. I've found a simple solution:
Turn the car off, and turn it back on. Some how, that resolves the issue. I can give it a little throttle, and it goes back to my 790rpm idle smooth as butter.

Does anyone have any theories on what may be causing this? Turning my car off and on again every time to resolve this, is obviously less than optimal..

(Other details):
1 bar map sensor
Maf turned off appropriately
VE being used

Thanks,
Andy

 

Post a tune please. My gut --

1. your proportional integral and derivative idle corrections are set up still stock. Your motor is 25% bigger and reacts differently, needs different pid values.

2. Your transient fuel likely not touched, causing very rich idle conditions and tip out.

 

I Agree. Post the tune and a datalog and we should be able to better help you. Its a shame that there are tuners like that. That is the main reason I learned to tune on my own.

 

Why Im doing the same thing.

 

1. You are correct. This was never touched. I went ahead and just added 25% for a quick troubleshoot, issue persisted. Then again, I have no idea how this should be set.
2. Also not touched, left it alone. No idea what this should look like.

If you knew what I paid for it, you'd puke. I originally went in and asked for a speed density tune - he insisted that I stick with MAF for now.... me being the newbie that I was, and letting the "pro" handle it, I agreed. After I got my car back in my hands and drove it around, I made nothing of it, as I just wanted to get home. The next day I realized how I felt ripped off. The drive-ability was awful. Turns out, my MAF harness never worked from day one. So, what did he tune it to exactly? Oh that's right, NOTHING. He was making changes in the High octane table, which isn't even used when in SD mode. It's a long, crappy story. But in the end, everything happens for a reason....and that reason this time is, it led me to learning all this stuff myself, and the satisfaction I gain from being able to do it myself now is tremendous.

I will attach the tune. Thanks Darth/EWY, hopefully we can figure it out!

Ignore the VE table, I'm still working on smoothing it out.
Ignore the timing, I've set everything extra low to avoid knock while I lean out certain areas.
I will be purchasing a KS-4 Knock sensor - it's a m8 1.25 sized sensor, which will plug right in to the side (gen 4). Will this work? It's from Phormula. I intend to use it for my time tuning.

Criticize as necessary.

Thanks,
Andy

 

what throttle body and intake you running?

transient -- min fuel mg -- set to 0.015
transient - min rpm - set to 1100

idle proportional error LOW -- set to 0.8 g/sec per 100 rpm error. Example -- at 100 rpm, use 0.8 g/sec. at 200 rpm, use 1.6. zero out all cells 0 through 80.
idle proportional error HIGH -- set to 0.0625 g/sec per 200 rpm. Example -- at 100, use 0.0313. at 200 rpm, use 0.0625. zero out all cells 0 through 80. Pay attention to the extra zeros. You want it to react quick when RPM dips and settle down gently when rpm is high.
All the proportional tables... in gear, ac on/off and p/n

idle integral error LOW -- from cells zero through 100, use 0.04 per 100 RPM. For cells above 100, use 0.4 per 100 RPM.
idle integral error HIGH -- Use 0.005 per 100 rpm all cells.

your throttle IAC is way out of calibration. It's still stock, and your throttle isn't stock, so it's going to overshoot/undershoot some until that gets fixed. Assuming you are using a 102mm throttle, copy the table and move it ten cells to the right. If it's a 90mm throttle, move it six cells to the right. That will be reasonably close to tweak idle.

After making that IAC change, if it tries to idle really low, it will need more base idle airflow.

Underspeed spark, from -1000 to -300 set to 14 degrees. From -300 to -100 interpolate down to 10 degrees at 100 rpm. then from 100 to zero, interpolate from 10 to zero. Your overspeed table is fine.

All of that combined may cause it to idle high and hang, but it should kill the stumbling. if it hangs, then it's a matter of reducing follower and cracker airflow and getting base airflow right so it finds itself earlier.

All these changes combined may cause it to hang on deceleration, but should stop the stumbling and result in improved idle stability

 

Fi-tech 102mm Cable - it's actually a very nice piece. Has all the provisions.
Fi-tech fab aluminum - gets the job done. Runners are too short. 5.25"

Do you suspect maybe the throttle cracker should be messed with?
Or perhaps the screw on the TB itself that keeps the blade open a little more?

Thanks,
Andy

 

I will make these changes tonight. Currently at work. Will report back with what I experience once I get it all configured.

Thanks for your detailed help!! Much appreciated,
Andy

 

Screw may need to be adjusted, but see what the warm idle iac counts are first. If they are high, then yes. If they are down between 30 and 60, I would not worry about it

 

You'll need more airflow in the idle throttle follower values too.

Tuning return to idle in an IAC car is VERY FUN.

 

 

If the spark underspeed fixed it, might be best to leave it be. Best test is to sit there at a dead stop. Rev, monitor return to idle. Coasting to a stop engages the cracker, etc. At a dead stand still, throttle stabs and returning to idle will tell you how your PID's for idle speed control are doing.

So, while the car is good and warm, stab the throttle. if it dips and recovers, or goes into a few oscillations before settling back down, do the PID changes. The settings I posted earlier are the result of sitting in my garage for hours doing this with a light clutch, alternator-only accessory set up, and SD, which is about the worst case scenario, because the engine is so responsive. I've used them on a few dozen tunes that would not return to idle well, and they work almost universally. Especially for that last annoying 100-200 rpm dip that you can't correct with the cracker and follower.

if it doesnt and just returns to idle smoothly, I would say you got it and not do anything else.

 

I've been in many an empty parking lots stabbing the throttle in neutral...

Also, you should throw it into neutral and coast down (on a backroad) to see how your areas above idle are and if your cracker needs any adjustment.

I would make PID changes last. A/F at idle and just above idle first... with timing next, both over/under and the idle/drive spark timing sync'ed up (like 22 deg idle timing... you want something like 28 just above it when you stab it in the higher load fields and higher RPM columns, but something that steps down to 26-24-22 in the lower load fields and as you return to your 800 RPM column), and then the cracker/follower tables. Follower, with the large TBs, needs more airflow even after you adjust the IAC transfer table. They go from a lot of air to not much really fast and it chokes out the engine. So you need the slower IAC to react faster and stay open longer (first to open bigger and then to decay more slowly).

 

Understood! I will see how it acts with some more driving after setting the underspeed as I did earlier.

lol! I have to admit, some of this is a little above my head right now. I'm going to keep reading this over and over as the days go and I know it will eventually make proper sense as I learn to tune more and more.

Seriously both of you, thank you so much for your time!!

 

We're both named Jake btw. That's why we're awesome.

 

Lol!

Actually on these larger engines I have found 16-18 degrees idle spark is best and drive spark tables are completely different. Need to set the max speed for the idle tables super high like 400 mph so when you put the clutch in it goes to the idle tables.

Idle regions in the main spark tables in mine are 24-28 degrees. Idle tables are 16 degrees, except the 0 and 400 columns which are 31 degrees which makes a great stall saver.

Lower idle spark allows you to set the under speed more aggressive, which provides a big torque bump when idle dips.

 

I run 18 degrees on my car for idle. Helps with the NOx fumes.

Most big cams actually need a lot less idle timing than you think. And my 400 column is set at 40 degrees as a stall saver.

 

this is awesome info guys. im in the middle of tunning my ls3 with a vengeance racing kaotic cam holley highram intake and 102 throttle body. car has a th350 trans im guessing this info will help my idle and just off idle tunning?

 

It should.

I should probably make a youtube tutorial on this. I'll add it to the list of things I said I'll do and never do.

 

that would be awsome