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Car dies at idle when AC is on

 
Old Mar 5, 2019, 01:42 AM
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Car dies at idle when AC is on

Trying to keep the car from dying when the AC is on. Tried playing with the idle tables and noticed some improvement, but it still stalls. It happens more often when it is hotter outside and even when cruising through a parking lot. Attached are screen shots of my idle settings, a log, and my bin. Running v7 - 96531706-TephraMod-phenem-sd

--edit--
Forgot to explain that this log ends with me pulling into my garage with the AC on, sitting at idle, then the car dies out on its own. This does not happen when the AC is off.
Attached Thumbnails Car dies at idle when AC is on-2019-03-05_2-36-43.bmp  
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Last edited by bpk1337; Mar 5, 2019 at 02:05 AM. Reason: Forgot to save .bin before uploading
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Old Mar 5, 2019, 06:38 AM
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Did this start happening after you changed something on the car?
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Old Mar 5, 2019, 08:48 AM
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The car was rebuilt from the ground up and a lot of work was done to it at once. It's hard to point to any one change that may have caused this. Brand bottom end, valves, springs, rebuilt transmission, new turbo, ac compressor.
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Old Mar 5, 2019, 10:39 AM
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Assuming the base map, vacuum lines, etc are okay, we Usually we start with the BISS, since it needs adjustment after mods. Then test the IACV. Then keep working down the list. It's always something super simple that drives is nuts.
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Old Mar 5, 2019, 11:16 AM
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Haha yeah I know what you mean about the simple stuff. Thanks for taking the time to try and help! The BISS has been set using the SAS mode in evoscan. The IACV has been ohmed out and it passes. I have also verified that it moves in & out with the key on. All vac lines are new, egr removed, and nipples capped off.

Base map should be close enough? As I said before it runs decent with the AC off. I'll admit that I am no expert in tuning though so if someone wants to check the logs and/or ROM (bin) file I will be eternally grateful The voltage looks like it might be low with AC on. I am not sure if the voltage with AC on is normal or not. With AC off it usually hangs out at above 13.5-14 volts. With ac on we're getting low 13's sometimes high 12's (Then less than 12 after the alt shuts off).
Highlighted in yellow is the moment right before the RPM's start to fall and the car dies. There are a few instances earlier on in the log where the car almost dies but is able to catch itself and rpm comes back.

(Double click on the image to use the magnifier to zoom in.)
Attached Thumbnails Car dies at idle when AC is on-2019-03-05_12-04-05.bmp  
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Old Mar 5, 2019, 12:08 PM
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Just post you AC-Off Neutral and AC-On Neutral tables, which are the 1st and 3rd tables in your previous picture.

In looking at my 88590015 EVO IX ROM when you go from AC OFF to AC ON the initial step values get lower so I assume this is subtracting from the Lookup Table. If that is correct then when I cut the AC ON I am not subtracting as much from the lookup table as with the AC OFF.

When I look at the 96531706 rom it seems to be the opposite with the AC ON step values being higher than the AC OFF step values so I assume this is adding to the Lookup Table.

If I look at your values for 180F for the AC ON and AC OFF tables you have the same value of 35. What this means is that no matter whether or not the AC is ON or AC is OFF the IAC is not going to change at 180F, which is likely why it dies. When you turn on the AC it places a load on the motor so you need the IAC to open more to offset the load an make the car maintain idle.

Last edited by 240Z TwinTurbo; Mar 5, 2019 at 12:23 PM.
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Old Mar 5, 2019, 12:13 PM
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AC off neutral = 1
AC on neutral = 3
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Old Mar 5, 2019, 12:56 PM
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My first recommendation would be for you to specifically search the relationship between Table 1 & Table 3 as it relates to the "Idle Stepper Lookup Table." If I pull up the stock 96531706 ROM, Table 3 values are higher than Table 1 values and I have listed them below. So what this would SEEM to indicate is when you turn on the AC it adds steps to ISCV to allow more air to bypass the throttle body so you maintain idle. If you want to do a quick reality check, take your Table 1 values and paste them into Table 3. Then add the "Difference" to them that I have listed below.




Sometimes it is better just to start with all of the stock values (for everything) instead of jacked up values that someone else created. FWIW, I just swapped over from an older V5 ROM to the V7 rom and I only had to slightly change these 2 tables for my idle to be perfect and I have 2.15L/R2 cams/ported head/ported intake/70mm TB.
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Old Mar 25, 2019, 12:02 PM
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Wanted to update my post in case someone else has the same problem. I noticed that by ISC steps were the staying the same regardless of how I changed the tables numbered 1,2, & 3 in my previous posts. The change that worked for me was to update my "Idle Stepper Look Up Table". I noticed my scaling settings were very strange so I changed them back to stock. After that I increased the last column on the right by about 5% and smoothed the next column for a nice transition. The car's idle with AC on is solid now.

(The car has FIC 1050CC injectors, walbro 255)

Only thing left to fix bucking at parking lot speeds. Will probably start a new thread for that unless someone has ideas.
Attached Thumbnails Car dies at idle when AC is on-2019-03-05_2-36-43.bmp   Car dies at idle when AC is on-2019-03-25_11-50-23.bmp  
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Old Mar 25, 2019, 05:35 PM
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Originally Posted by bpk1337 View Post

Only thing left to fix bucking at parking lot speeds. Will probably start a new thread for that unless someone has ideas.
My car has been doing that for years. I have yet to find the cure.
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Old Mar 25, 2019, 05:50 PM
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Originally Posted by kaj View Post
My car has been doing that for years. I have yet to find the cure.
Are you also on speed density?
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Old Mar 25, 2019, 06:56 PM
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No, sir.
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Old Apr 2, 2019, 05:49 PM
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Your tables should NOT be in steps. They should be in "demand %"

Go read MRFREDs ISCV disassembly thread.
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Old Apr 2, 2019, 05:58 PM
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FWIW: My car actually "bucks" at throttle tip in, at low RPM, no matter the situation. Parking lots are just most noticeable because I don't usually give it enough throttle to get past it. Seems to be anything below 2k RPM.
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Old Apr 8, 2019, 01:45 PM
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Originally Posted by kaj View Post
FWIW: My car actually "bucks" at throttle tip in, at low RPM, no matter the situation. Parking lots are just most noticeable because I don't usually give it enough throttle to get past it. Seems to be anything below 2k RPM.
Iíve been chasing a similar issue on my VI for a year.
Adjusting the TPS voltage and open loop thresholds has helped but I think my clutch is adding to the issue as it has a racing flywheel.
Sometimes adding fuel on tip in can help, if it is a misfire or lean tip in.
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