Surging idle issues - please help!

[tunedportcj5]

Here is what I am working with....

'98 Z-28, a4, 3500 stall, TR TRaK cam (231/234 .640/.590 112 LSA), Comp 921s, Fast 90, NW90, SLP LTs, SLP ORY, 3.73s

OK, this is driving me crazy. I simply cannot get my car to achive a solid steady idle in P/N. I have spent almost 2 full weekends with dozens of different tune configs and have not been able make ANY progress. The weird thing is that if you put the car in gear, 90% of the time it will NOT surge and idle nearly perfect (or acceptable by me). But once it goes back to P/N - its hunting season.

When the car is cold started, it will fire right up and it will idle PERFECTLY ~900rpm for 30-45 seconds. Then it starts surging like crazy, 400-1500rpm a few times and then it will die most of the time.

The only way I have ever been able to get to idle perfectly in P/N is to use the bi-directional controls and demand around a 16:1 AFR... If I do that, it will idle all day. It just seems way too lean to me, there has to be another solution.

I have read nearly a 100 threads with this same symptom and I've tried it all. Most point to the IAC Effective Area and Desired Airflow tables. My desired IAC flor rate is usually 1/2 of the Calculated Air Flow Rate.

I have modified the IAC effective area to help equal out the two variables. The the car just goes to hell... it makes things way worse!

I will attach my current tune - everything off idle my car runs awesome.

Please let me know that you think - your help will be GREATLY appreciated.

Download Tune

Thanks,
David

[SSpdDmon]

try this one...

The changes I made were:

Base Spark P/N (looked high - usually 22* is a good place to start)
Filtered RPM Airflow - 98's had this zero'd out for some reason...
Learned RPM Airflow - Anything in the 20 or 40 rpm rows will cause an issue on a cam'd car as well as too much at the extremes...
Direct Airflow Correction - reduced 25% for a start. When rpms drop or rise to extremes, the values greater than 200rpm usually add or subtract too much air. That's one of the reasons why when it's low, it shoots up high and why when it's high, it drops down low.

After looking at your desired airflow, you might want to try the RAFIG and RAFPN again from a cold start each time. Ideally, the Desired Airflow In Gear should be slightly higher than the P/N because the load of the converter/drivetrain is placed on the motor in gear.