tunedportcj5

iTrader: (18)

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.

Here is my current tune - Download Tune

Thanks
David

GOaT Cheese

Try unplugging the MAF sensor when it is acting up. When it is cold the PCM doesn't look at the MAF, if it clears up with MAF un plugged, check for dirt or debris on the hot wire.

1LoudTA

iTrader: (11)

my trans am did that all the time. i found out that the tune i had in that car was a little fuckd up. i dont know if it has anything to do with this but i had a 2000 and i used someone elses tune as a baseline for mine and i found out that my car was programmed for 28lb injectors when it had the 26lbers... that was one issue.. another thing was the voltage on my tps was a little low, at idle it was like .4v and it should be around .6v. so i adjusted that. also, did you drill out the hole in your throttle body blade? sometimes that helps out idling issues with the car.

kenkaru

Try using BiDi controls and clearing the fuel trims. I did this yesterday morning and it has cured my frustration. I've never seen anyone mention this important step so I'm wondering if it's just a '98 thing. (I have a '98 too.)

I used to have similar problems with my car where changes would make it idle crazy or not at all but since I cleared the fuel trims it's like I couldn't make it idle like crap if I wanted to. The desired AF table seems to be numb now. It's wacked. Hope this helps.

My90Iroc

iTrader: (26)

Ever since I installed the 90/90 I've had this problem and I've been working on a couple other 90/90 cars with idling problems that were professionally tuned. First I put the cars into speed density and open loop then try to get the iac counts into the right resolution range by adjusting the throttle screw and idle airflow tables. I've been able to get the idle better on all the cars this way but still not consistent. It'll be good one day and terrible the next. My next attempt will include adjusting the iac motor parameters and decrease how much it tries to compensate and how fast. Hopefully this will get rid of some of the erratic behavior and help the computer learn and compensate better. I'll also adjust the timing to see if that helps at all. I've been too busy lately to really mess with any of the cars but hopefully I'll get some time to this weekend. Keep us updated.

tunedportcj5

iTrader: (18)

TTT.... Anyone want to buy a fast surging '98 Z28?

TXCAMSS

iTrader: (60)

When you make the changes to the effective area to get the desired and dynamic airflow to match, make sure you give the car some learn time. It will run like crap initially because these changes also directly affect the base running airflow. Once you get the effective area lined out go to the RAF and get the LTIT/STIT in line. I also do a PCM reset each time after flashing the PCM. This allows the LTIT/STITs to start at "Zero". If your LTIT are max out at their limits (adaptive idle) the car will hunt it's *** off.

I also bumped the timing in the lower areas that the car shouldn't be in such as 400-800. I set them to 32-36 and it helps the dip recovery. Someone here (Meant or Guits I think) recommended that and it does help quite a bit.

Good luck!

02sierraz71_5.3

iTrader: (2)

Aside from your fueling being off at idle a big part of it is spark. Adjust the under/over speed spark tables they play a big role with it searching up and down. Idle needs to be at least 900 rpm till it warms up then no less than 750
BTW: idle tuning is the hardest out of all of it.

Slowhawk

iTrader: (12)

I have the same problem sometimes on 98 cars. Runs good 1/2 the time and other times it will surge like a bitch Seams like the cars that do it all have TSP Cams too

foff667

iTrader: (2)

the origonal poster has a TRak cam made by thunder racing fwiw.

Personally I had a tsp 231/237 cam in my personal car through an A4 with 2.73 gears that had no bucking or surging by the time I was done with it.

kamikazematt

any updates on this? i'm going through this also?