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Haltech Air Conditioning idle issues

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Hi. Currently tuning an Elite 2500 on MKIV Supra with 2JZGTE. Originally the AC idle was perfect but after a dyno tune, the AC wants to idle at 1500-1800rpm when active State vs the 850rpm idle set point. Car has the IACV on it and factory manifold. Car idles perfectly fine with AC turned off at set point of 750rpm. No settings were changed before and after dyno tune to the idle settings.

Other issues I’ve got are:

1 - car doesn’t seem to want to decel cut properly. IE when I am off gas cruising to a stop to let engine brake, it isn’t braking.

2 - sometimes I get rev hang during shifts (6spd manual)

If no settings related to idle were changed and idle went up 700-1000 RPM, it sound like something may have changed mechanically or electrically. My experience with 2j IAC's also suggests it may be the problem. I feel like they've ended up needing replaced on most of the ones I've tuned so I love DBW converting them.

If the car also isn't decel cutting, which is likely related to your rev hang too, perhaps throttle isn't returning to where it used to, so idle isn't reliably responding as expected either?

If an ECU doesn't see TPS below activation thresholds, functions may not become active, so I'd double check logged TPS as well as the max throttle values to enter decel fuel cut and idle.

I’ll have a look at my recent logs. I haven’t had a repeat of the idle issue since that day and unfortunately it was logging that day as I was just driving home from work.

I’m also wondering if the throttle cable is sticking open a bit. I’ll check tension on it.

I’ll check those throttle values as well. Because I’ve noticed that sometimes the Haltech is saying that idle state isn’t active due to running state. I’m using the base map values which is why I’m thinking it’s more a mechanical issue than tuning.

Well I'm glad to hear it hasn't been happening.

When the AC is on the engine bay is likely getting hotter which can be a factor in things getting stuck so that's a possible factor.

Setting throttle closed and open position voltages is generally required per car in case you're still using base file values for them. I know this may sound odd if you're using a factory part, but there is car to car variation and if it's preventing the ECU from detecting when throttle is closed, that may inhibit functions that are enabled below a certain throttle opening like idle and decel fuel cut.

First thing before first start was always to calibrate the TPS. So it reads proper closed and WOT.

I’m going to review some of my last few logs to check if tps is showing the throttle staying open on decel or idle.

OK sounds good.

I'm going to close your duplicate thread in the standalone section so we can focus on helping you here.

From reviewing the logs, my car is only entering closed loop idle and decel when the TPS registers below 0.5%. Anything above that and I get “Open loop due to engine State running.”

Is there a place to adjust this to say 0.9% tps? Or is this a mechanical issue to fix because the tps isn’t always showing below 0.5% when my foot is off the pedal either in decel or at idle?

This ECU isn't my specialty, but it seems you want to adjust TPS so it reads 0.0% when off throttle to reliably enter idle mode, and that's generally what you want on any ECU with a drive by cable setup.

Under Decel Fuel Cut if detection mode is TPS, there is an Arming TPS value you can set to 0.9% if you wanted to, but you may still need a TPS reading of 0 for idle mode to work on a drive by cable engine, so it seems you might as well leave decel arming at 0.5%, get TPS returning to 0.0 reliably, then test.

Again, this ECU isn't my specialty, so that's just what I would try.

So I recalibrated my TPS. Seemed to completely fix the decel issue. I also can adjust the zero demand TPS in engine configuration.

However, the AC issue wasn’t happening for a while but has started happening again . Sadly I wasn’t datalogging! So frustrating. It did the idle raise and hang at stop or coming to a stop. Additionally I noticed that it would hang around 2000rpm and then the car would slightly jerk and the rpm would drop occasionally to the correct settings. I’m almost certain this is a throttle or tps issue and not a IACV issue.

Another new problem popped up as well. When the headlights are on and activating the brakes I get a p0641 and p0698 DTC. I was able to log this and see that it causes a voltage spike when activating the brakes. I do have the brake switch wired to AVI4. I noticed this when headlights were on and threw the code. The voltage spike can be seen on other AVI inputs whether lights are on or off.

However the brake switch does not share sensor ground. It simply goes from the switch to the AVI. Haltech shows on their PNP harness it wired to AVI4. Am I missing something?


I'm glad to hear that first bit worked, but sorry to hear your issue has returned.

It sounds like logging to make sure you don't miss it will be required until this is surely resolved. Perhaps you can set up logging that will give you the data you need, without logging absolutely all the time i.e. over 500 RPM, under 8% TPS, with a delay of a few seconds. If you're sure it can only happen with AC on and the AC button is wired to the ECU, that's another option for gating logging. If the system you're working with doesn't allow for sufficient gating of when it records to make small log sizes, worst case you wade through some bigger logs and toss the ones you don't need.

I like to install a button meant to be pressed to indicate something to review in a log later. You'd press the button when idle suddenly increases. That way you can immediately spot it and avoid scrolling through large files to find specific occurrences. It can simply be a wire from chassis ground through a momentary button, to a digital input with the pull-up resistor function on in software, so an easy wiring project, and basic buttons are cheap. If you already have a CAN keypad with an available button, or a button you can use for this as well as its regular purpose, that's another option. You just want to choose something you can jump right to during log review.

In terms of your brake switch issue, I use other brand plug and plays on MKIV Supras which has not done this, but I'll try to take a stab at it. It sounds like you're saying you have it wired as your manufacturer suggests, but usually I'd expect a 12V switch to be wired to a digital input rather than an analog voltage input. If you're sending 12V into a circuit meant for 0-5V range, that could be the problem. I'm not clear why it would matter if the headlights are on or not, unless wiring is not as expected. This seems worth a quick chat with Haltech, and they can likely give you a simple solution.

Yah the brake circuit is 12V but the AVI can accept up to 20V.

I sent a log to Haltech and hopefully they will get me a response.

I am not sure if this is related, but it sounds like you an electrical current problem. When the wires are not big enough to handle the required current, the voltage drops causing the problem. I had a similar problem where my cruise control would not work if the HVAC fans were on high speed. The problem ended up being that a braided ground strap to the cabin was not reconnected after some engine work. The other symptom was that when I operated the window, the cruise would kick off. Both the HVAC fans and the window motor are high current demand devices.

Hope this helps.

Any chance the brake switch isn't just completing the switch circuit and it's actually being used to pass power to the brake lights, rather than being relayed?

So what I found was one of the AVI inputs was causing a voltage spike. I removed that wire and now the issue voltage issue is resolved.

I have been trying to log the AC issue. I ended up adjusting my zero demand TPS to 1%. I’ll continue to try to log the issue if it presents itself.

Sounds good. Thank you for the update.

So I was able to grab a log of this:

It definitely is a weird intermittent issue. The rpm raising happens only during times the AC is active. It will cause when off throttle for the rpm to raise. This is whether I’m in motion or stopped.

In watching the log I can see the idle out raising as high as 60% but also see the tps sensor reading 4-5% throttle even though im off the pedal. If I turn off the AC the tps will drop to 0.4%.

Would posting the log help? I’m at a loss.

What does the throttle show with engine off?


Might be worth trying to mount a dial gauge to confirm there is no physical movement on the throttle when the bypass is at higher duty. If the TPS is low to high signal voltage you wouldn't expect it to pull up is signal earth is tied to the block unintentionally.

TPs is wired to signal ground. The IACV is wired to 4 stepper motor outputs. Again this only occurs when the AC active and it is somewhat random.

Running more detailed logs the TPS is fine. It is dropping to 0.1-0.3%. However, my idle state is saying: “open loop due to engine limited active”

This “state” is causing the car to keep the rpm’s very high when it should either be in decel or idle state. The TPS is at 0.2% which is under the zero demand 1% setting. The wideband is showing super lean as if it was in decel.

You need to post a copy of your tuning map. Or we can just ask lots of questions. What are all the settings in the Main Setup->Idle Control Function->Idle Control Tab?

Any chance you have some kind of manifold leak that is only active when the A/C is on? Say a control valve that uses vacuum, but is only active when the A/C is on?

Here are a couple of log files of the car having the AC issue. The engine doesn't have vacuum leaks and when the AC activates it doesn't always cause the issue. It is somewhat random. Also if the car is having the rev hanging with the AC activated, you'll see in the log that if I blip the throttle (cable) it will cause the car to fix the error.

Attached Files

Looking at that log, I see the Rev hang happens when the vehicle is moving at 50 mph. Are you expecting idle control under those conditions. If so, you might want to reduce your ignition timing from 34deg at 1800 RPM / -62 MAP, as I think that is one reason for your rev hang. The other is the Idle Control Output goes up to 55% when the target RPM is 950 (its is only 9-12% when it's active at 850 RPM target). I think your Idle Control Base Output table probably needs modification for when the target RPM is 950 RPM.

I am not expecting idle control at 50mph.

When you are speaking of the Idle Control Base Output needing modification, are you thinking the output is set too high or too low?

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