1999 LS1 T/A tuning questions??

[weston]

hello, i have a 99' t56 trans am LS1 heads/cam build and i have been going back and forth with a tuner the last 6 months with these problems ive had just hoppin on here to see if someone may be able to give me some insight. The current problem im having is that the car will have a hanging idle when letting off the clutch especially with the AC on it will do it occasionally with the AC off however if i have the AC off the car seems to have a rough idle when i turn the AC on the car idles fine. im guessing its something to do with the AC bring more Vacuum into the intake but i could be wrong. Ive explained these problems to my tuner and he keeps telling me to look for a vacuum leak however i have removed the intake replaced every single sensor possible MAF, MAP, TPS, IAC, 02 sensors and it still does it. The car also keeps going through TPS sensors every couple hundred miles or so. The reason i belive it is a tune issue is because the first time he tuned the car my problems werent as bad it wasnt until the 2nd time back and had him do some adjusting that the car seemed to have gotten worse. i will attach my tune file along with a data log to see if anybody can give me some insight.

Thanks, Weston

1999 Trans am T56: rebuilt LS1, 231/234 cam, 243 heads, longtubes along with supporting mods.

[kevin87turbot]

It doesn't appear to be a bad tune, but there are several things that I would do differently.

The idle spark is 22 degrees. You might want to lower it a bit and make the over/under speed spark tables a bit more aggressive so they can do their job.
The min spark is set to 21 degrees from 0-800 rpm...which is ok...it'll catch the engine when it tries to drop below target idle. However, the over/under speed tables should be able to handle that as well.

It's currently running on MAF only, but the fuel trims are ok.

You can adjust the Min Air table and/or the AC Compressor torque model if the hanging idle bothers you. It appears that the Min Air table is just a bit too high based on the logs you loaded. Be careful with those adjustments though. If you reduce them by too much, it will stall.

[SiriusC1024]

I agree on the spark being to high. Coupled with that lower idle rpm. Idle airflow is pretty high, too. What are the cam specs exactly?

However, I disagree about the fuel trims. They are pretty poor.

As far as TPS make sure you're using genuine parts and getting the correct supply voltage then follow this procedure:
https://www.pcmofnc.com/2021/03/05/i...throttle-body/

The only thing the AC is doing is causing drag. This would make the idle more stable on its own by damping over/underspeed rpm changes. See, idle speed, airflow, spark is causing higher torque than you need, so any idle correction being made by the ECU is exaggerated.

[edcmat-l1]

Another one done by someone who doesn't know what they're doing. 2 or 3 different parameters/tables is all you need to see to know whoever (fill in the blank) doesn't know what they're doing.

[SiriusC1024]

DFCO enable temp, PE enrichment, MAF DTC's, Min fuel transient qualification, RPM cutoff/resume, EGR diag enable, mismatch between primary and secondary VE.

What do you see?

[weston]

Ok I?ll start with the basics if I change the idle rpm to let?s say 850 do I have to adjust any other table suck as airflow or spark etc. I thought 950rpm was high as well. I gave the guy another chance at fixing the car and he made it worse so I?m attempting myself. Thanks.

[SiriusC1024]

Yeah you'll have to adjust BRAF down, assuming it was accurate for the 950 value.