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