Nistune Forums

I have a 97 240sx with a turbo KA24DE running with a 96 feature pack manual ECU. I turbo'd the car a year ago and had it tuned by Martin at RS Enthalpy. When he loaded his base tune on the car it started hunting for idle. He was pretty sure it had a vacuum leak. We used half a can of ether all over the intake and came up with nothing. So he added fuel to the fuel map in the bottom left 6 cells so that it idled correctly and tuned the car. The car has ran great on 17 PSI since tuning. All AFR's outside of idle are perfect and have always been. Idle AFR's are always 18+ unless the motor is cold. Vacuum at idle fluctuates depending on how it's running but stays between 28-32 inHg.

Since then I have tried the following to remedy the lean idle:
Replaced IACV (new OEM)
Replaced AACV (new OEM)
Rebuilt the intake five times
Routed the valve cover breather to intake pipe pre-turbo and post MAF (thinking unmetered air was the cause)
Replaced and adjusted the TPS sensor, .48v closed and barely touching the throttle cable shuts off the TPS indicator in nistune
Removed all emissions and extra vacuum lines (only things left are Brake Booster, BOV, FPR and MAP switch)
Boost leak test (22 PSI, no leaks)

Long story short, I know the intake doesn't have a leak. None of the above has changed the Idle AFR's. However, even though all AFR's outside of idle have stayed the same my lean idle has gotten worse. It is to the point that I can max out the fuel map (@ 127) at idle and it still doesn't register on my wideband. I have done everything I can to correct this lean idle and have no ideas left. I read about a TPP Min that I could use to set a minimum load at idle RPM's but that option is not available in nistune for my ECU. I have even tried to restrict airflow by squeezing the hose from coldpipe to the IACV and AACV but that just causes it to lean out further. The ECU is fighting everything I do to try to richen up the idle. Is there any settings I can use in nistune to set a minimum injection time at idle?

Car Setup:
.020 over KA24DE block
Wiseco 9:1 pistons
Eagle Rods
3 Angle Valve Job
All ARP hardware
740 Deatschwerkz sidefeed injectors
Z32 MAF (draw through)
Emusa T3/T4 turbo (I know what you're thinking but I have 20k miles on it with no shaft play)

I have attached the tune (minus the extra fuel at idle) and a log of a short drive to work today. Any help would be greatly appreciated. I'm completely out of ideas. I know it's a long log but pretty much everywhere at idle it struggles to run. Right at the 12:00 mark the car got died because it wouldn't catch idle. I have to bring the car to idle in gear with the clutch out and it didn't work that time. If it comes back to idle too quickly it will die.

Compare the RS tune against the base tune for this ECU to find issues. Use file S14_KA24DE_72F0F_MT_FP_maps.bin for comparison and use the 'magnifying icon' to locate changes

The 0 section of the map should normally stay at 0. This is the closed loop flagged part of the map. It is quite strange to have this filled with '10' just to improve idle and low RPM areas

Volumetric efficiency tables are TPS vs RPM based, so only have effect on certain throttle positions. There is a limp of fuel around idle/take off here

Lowering the TP max table from
104 104 104 104 88 102 104 101 100 108 113 115 118 120 116 109
To:
25 25 75 80 88 102 255 255 255 255 255 255 255 255 255 255

See these first four columns. The default 104 value has dropped (likely due to the automatic injector resize having TP max ticked when resizing injectors in the software). So what you need to do is fixed up those first four values to be 104. Probably why you cannot get any more fuel (since it is limited by this table)

Recovery AAC duty has been increased. May result in increased idle. Try changing back to original values

What you can do otherwise is

(a) load the factory 72F0F tune and do File > Import Selected maps from file. Just select the basics to start with (K constant, TIM and VQ map). See how that goes. (or)

(b) Otherwise load the 72F0F factory file as main. Open RS file as comparison. Then 'copy' button and select maps as required from comparison to main

Remember to upload to ECU after doing either method (loading and copy button do not upload maps) and see how that goes

Sorry for the late reply, I will try all of that. Yeah, I did a couple very low RPM-high throttle scenarios to determine what my TTP max should be. I did realize that I had a tiny exhaust leak (wasn't audible) this weekend after replacing all exhaust gaskets with solid copper. I also replaced the IACV again with a used and working unit from a factory KA and kept the idle adjustment screw on it in it's original position. I have AFR's registering at idle again with the bottom of the fuel map reading all 10's. Now that the IACV was replaced again, It's very hard for it to catch idle and it backfires almost every time. Sounds like a gunshot.

Technically, I should have good AFR's at idle with the bottom of the map set to 0 instead of 10?

Thank you for your help.

Yes you should if you have it set back to 0 (and injection multiplier is showing stoich on cruise)

That is awesome! I returned the bottom of the fuel map to 0's and low load throttle response got much better. I also made the recommended adjustments to the TTPMax, load index no longer spikes. I swapped my new IACV back onto the car and dialed it in as per the FSM and idle and cruise AFR's are now perfect! A year long problem has finally been fixed.

Thank you so much Matt!