High Idle Switch Install

I have recently been on a mission to increase my AC effectiveness. Sometimes for work I need to work out my truck in 100deg weather (construction in Florida). Doing some research I came across a method that some trucks/vehicles used that I thought I would give a try. A high idle switch. Basically a button I can push to take the idle up from normal to a bit higher. In theory this should increase fan speed and pull additional air over the evaporator coil while the truck is parked and not getting the flow from being in motion. Apparently lots of work trucks/police/ambulance have this feature to help the alternator keep up with added accessories and help with AC during long periods of idling.

There were a few different methods I found. Some mechanical (physical lever to hold down accelerator, throttle body actuator, etc). But, my method will be from tricking the ECU into thinking the engine still needs to be warmed up. Best I can tell this post from 2009 was the first time someone did it. https://www.yotatech.com/forums/f2/high-idle-switch-anyone-198737/

When the coolant temp sensor reads lower than ~180deg the ECU thinks the engine is not up to ideal temp and will idle up to try to get it up. We can modify the output of the sensor to send fake data to the ECU to mimic this.

• Step one was to hit the junkyard. I didn't want to splice any wires for this project so I will be making a T-connector. I needed to salvage a few male/female ends of the coolant sensor and wiring harness.
• I was looking for Coolant Temp Sensor PN: 8942233030 (5.7L 2007). Found it on the Toyota parts website and it gave me a list of compatible cars. The ones I found were from Corollas and Camrys. There were about a dozen in my local junkyard.
• Here was my haul:

• Build my T-connector. A little soldering and I came up with this. Pin 1 (see diagram below) was connected straight through to carry the input voltage. Pin 2, the output, is where we will be adding resistance. Higher resistance = lower temp (See chart at bottom). The resistor will go between the two stripped ends. A normally closed relay will go between the red connectors, to be opened with a push button in the cab.
• To install in truck simply unplug the connector from the Coolant Sensor (front right of engine) and plug in connector in it's place. Then plug the other end of the T-connector into the female side of factory wiring harness. 10 second install.

• Here is a hand drawn diagram. Notice that the wire that goes to pin 2 now has two paths. One through a resistor and one through a switch. When the switch is closed the electricity will take the path of least resistance and output the true temperature. When the switch gets opened (thru a normally closed relay) our custom resistor will be part of the circuit.

• Next step was to figure out what resistance I needed to get the RPMs where I wanted. With a little testing I came up with this chart. You can clearly see as the resistance goes up the the temp goes down and RPMs go up. It's important to note here that when the AC light is on the ECU sets idle to 100-200 RPM higher to help power the AC compressor. I came across a random post that claims our compressors are at full output around 1500rpm so that was my target.

• I used the Torque App with a $25 Bluetooth OBD connector. I was concerned with the following data only. (Screenshot from 617 ohm resistance)

• Once I had figured my total desired resistance I soldered up a few resistors in series and soldered them into my T-connector between the green wires.

• I am still waiting on my relays to come in the mail but I tested the setup manually by connecting and disconnecting my red connectors. Best part is that if something gets messed up I can take the whole connector out in a matter of seconds and get it back to stock set up.

• Potential downfalls
  • Overheating - If you are in high idle mode and start to overheat it will be harder to notice because the coolant temp sensor is reporting so low. When high idle is active the temp gauge on the dash sits at about 1/8-1/2. It will still go up in the event of an overheat because the sensor itself will add additional resistance, however it may not toss a CEL or go into limp mode if left unattended.
  • Resistance needs to be high enough to simulate conditions for closed loop air/fuel mixing. I was not able to find an exact temperature where the truck goes into closed loop but all my testing kept it in closed loop, so it must be under 118deg.
    
  • P0128 - Reading in the FSM every time you start the truck it goes through an automated check to make sure the engine gets up to temp in the expected amount of time. Chart below. It basically calculated the estimated time to reach 167deg and then checks to see if the engine got there in time. It runs once per drive cycle. As far as I can figure, as long as you don't start the truck in high idle mode two time in a row you will not have any CEL. Will update on this though if that's not the case. (Diagram from FSM below)

• FSM showing resistance vs temp in coolant temp. sensor

• Connector/wiring diagram
• 

Resources
https://www.yotatech.com/forums/f2/high-idle-switch-anyone-198737/
https://www.toyotanation.com/threads/howto-high-idle-mod-ect-mod-5th-gen-t4r.1709633/
http://web.archive.org/web/20051102060052/http://www.midiwall.com/4Runner/ect.html

 

Great work buddy.. keep it up..

 

If it doesn't work you could get a gas pedal from a junkyard and it's connector. It would be easy to wire up a switch so you could toggle between the pedal and a variable resistor so you could just adjust the pot to get the RPM you want.

 

This is a great idea. Probably a safer way to do it than my method, you don't have to trick the ECU.

 

Great job!
I often wish I had a setup as I did with my Dodge CRD. It would idle up for winter idling or in the heat for the ac...more than that, I miss the setting that allowed me to set it to hi idle, take the key out and lock it up with the dog in the truck. It would keep running with the ac on, but if someone broke in to steal it, the truck would shut off as soon as the break was applied to shift out of park.

 

What about a electric fan?

 

Looking at some wiring diagrams more it looks like this may have a few more hurdles. The coolant temp sensor is a simple circuit (only 2 wires), the Accelerator Position Sensor has 3 wires on the connector. I didn't go too far down the rabbit hole but there must be some more going on than just reporting the resistance. I'm not smart enough to figure that one out.

The high idle button plus my 12vSolutions remote start allows this. The remote start has a "pit stop" mode, that lets you remove key without turning off car.

This is on this list but only helps with the airflow side, not the compressor rotation issue. Also this mod costs under $10. Electric fan is a tad bit more expensive. It may still be in the future though if I can find a budget option.

 

Chrisf11, thanks for the info about the 12vSolution system. I'll check it out.

 

Always happy to recommend a product I am happy with. There are plenty of cheaper remote start kits on the market. In fact I think the kit that 12volt uses is less than $100 if you buy it directly. What you are really paying for is the wiring kit set up and ready to install. The entire install process is opening up the steering wheel trim and knee plate, then unplugging 3 connectors and plugging then into the remote start harness. Literally takes minutes.

Without the harness you'd be splicing into your factory harness. Dozens and dozens of splices. Hours of work. With the harness you can also remove the system just as fast as you installed it (ie. in case you are having issues with the truck and want to eliminate the remote start as a potential cause).

I also recommend the long range remote add-on. I've stopped carrying my factory remote. I was only getting 50-100' of range with it. Now I can start from inside my house, office, and even from deep inside home depot.

Happy to answer any more questions. I am not affiliated with then, just a happy customer.

This is the one I used. I paid $410 shipped with the long range option (memorial day sale)

https://www.12volt.solutions/products/2007-2010-toyota-tundra-plug-play-remote-start-kit-dot-key