Car idle too high

[yurk3]

Hello everyone! I’m having a different problem with my Toyota 86 and I’m hoping someone has an answer to. After I start my car up and give it time to heat up, usually the car drops its idle to 700-800 RPM, but for the past couple of weeks my idle goes to 1100 RPM. When I do research on this issue I find that it could be the throttle body being dirty or the MAF sensor. I tried cleaning both of those but nothing was different. I also tried replacing the throttle body but that didn’t fix anything. Does anyone know what else could potentially be the issue?

The car is a 2020 Toyota 86 base model with 82000 miles
The last servicing the car had was an oil change and a transmission fluid flush. I don’t think any of those should effect the idle of the car but in case it helps.

[sly]

A couple of possibilities come to mind. Are you sure you have no vacuum leaks? If you PCV hose is loose or one of the hoses on the throttle body are not fully seated, it could cause this. Or it could be the catalyst not heating up or detecting that it's heated up. When starting the engine, you will get an advance on the exhaust valves to warm up the catalytic converter for emissions. If your timing doesn't retard to normal or the 02 sensor is not giving readings, it could stay at fast idle longer trying to warm up the catalyst. You could also have a bad temperature sensor and the ECU thinks the car is colder than it really is.

I assume you have no check engine light? Are there any other symptoms or have you changed anything else on the car, even if it seems inconsequential?

[yurk3]

No I don’t have any check engine lights. The last thing I did was the transmission fluid, which I checked how much to put in and there haven’t been any issues from that. As for the lines they are clamped on but I can check to make sure they don’t have any cracks or holes. As for the temperature sensor where would I find this?

[yurk3]

Also I forgot to add this and idk if it will help, but the cars idle RPM will drop as the car heats up more. After I drive it for a while and everything gets to operating temperature the RPM will stay around 800-850 RPM

[sly]

Definitely sounds like a problem with the temperature sensor or the circuit to it or possibly the oxygen sensor not heating up. If the car does not see that it's warming up, it will stay in fast idle. If it can't see the engine warming up, it will stay in open loop mode which has a fast idle. If you wanted to throw parts at it, I would replace the coolant temperature sensor and possibly the o2 sensor. But better, it should be diagnosed first by connecting a monitor to it and data logging the sensors to see which one has failed or is slow to respond.

[callisto]

Does the behavior change if you pull the battery for a minute to reset the ECU learned idle and throttle parameters (if you didn’t pull the battery during that work)?

Does it persist (or CEL) if you do the idle calibration process (start it after 8-12h off and let it idle for half an hour, off for a minute, start and idle for 5 more)?

[yurk3]

Hi,
Yes I pulled the battery and I also tried the idle calibration but both of those changed nothing. I haven’t checked my O2 sensors though so that’ll be my next plan of action.

[yurk3]

Hello everyone, so I scanned the car and the O2 sensors were giving the proper voltage. One thing I noticed is when I scanned though I did get a code, U1201. Is this code potentially the reasoning for the idling being so high?

[sly]

That's a CAN Bus communications failure code. It's possible that something is corrupting communication to the ECU. Are there any aftermarket mods to the car? It could also be loose ground connections.

I'm seeing that it could be caused by a loss of communication to the ABS module. Perhaps triggered when you disconnected the battery. Can you clear it and does it come back? Do you have the traction control light indicating an error? If you lose traction and stability control, it could possibly cause a fast idle if the ECU is in limp home mode to keep it from stalling.

[yurk3]

So aftermarket parts at the moment I only have a cold air intake an upgraded coil packs. These were both installed last year. There’s no traction control errors lighting up either.

As for the ground connectors, I know there’s 2 up top near the battery and fuses but where would I find the others? I want to make sure I clean all of them thoroughly. On top of that, I was told to use some medium or fine sand paper when cleaning the grounds, would you agree that this is fine or do you recommend something else?

[sly]

How long have you owned this car? Reason I ask is that it will idle high sometimes if the ambient temperature is cooler. On warm days, mine will idle high for 1 minute on cold startup and then drop down to 850. But on cooler days it may stay at fast idle for quite a while until dropping down. I'm just wondering if this is normal behavior that you might not be used to or if something is actually wrong.

You say that when you drive it and it warms up fully, it will drop down to normal idle speed. Does it ever come back up during that run or does it stay at normal speed? I'm not suspecting any grounding issues, although it's not impossible... But I'm wondering if this might just be normal behavior.

[yurk3]

I’ve owned this car for almost 2 years now. It will sometimes idle higher in cold weather but never like this before. Most days by me this summer has been like 80-90 F

And yes after a good 5-ish minute drive the idle will go to 700RPM and stays there until I turn the car off and start it back up again.

[Muskoka800]

Originally Posted by yurk3

So aftermarket parts at the moment I only have a cold air intake an upgraded coil packs. These were both installed last year. There’s no traction control errors lighting up either.

As for the ground connectors, I know there’s 2 up top near the battery and fuses but where would I find the others? I want to make sure I clean all of them thoroughly. On top of that, I was told to use some medium or fine sand paper when cleaning the grounds, would you agree that this is fine or do you recommend something else?

FYI, There are two small engine to body grounds, one on each side at the bottom near where the engine and tranny meet. You may need to remove the under tray to access them.