Idle speed increase if heater on

Ok. Mine is not auto. When I turn on my AC or defrost the idle speed does not increase, yes the ac loads the engine but it does not rev higher at idle. This seems to be only associated with the heater - regardless of the AC. Once the engine temp is normal engaging the heater no longer causes a change in engine revs.

 

My '85 Supra had climate control.

 

When I first turn on the heat in my 4R, after the engine's warmed up, the A/C light on the knob will light up. I just hit the button to turn the A/C and compressor off and continue driving with the fan and heat. I was told that one of the reasons for this early A/C - ON feature was so that the compressor bushings and seals will get lubrication during the winter months when the A/C is seldom used. This was a feature added for later vehicles.

My other vehicle is a 96' Jag XJS. This has the older style A/C. During the winter/cold months, you have to "remember" to occasionally turn the A/C on. Otherwise, you risk drying out the seals in the compressor requiring early replacement. It even mentions this in the owner's handbook.

 

Mercedes Benz also had it...but generally in the 80s you were using the good old fashioned "too cold / not cold enough / not hot enough / too hot" dials.

 

I know. I'm just goofing around.

Honestly, I prefer good old knobs. The Tacoma I had while the 4Runner was getting fixed had dual climate control, and I could have lived without it.

 

I actually had to look it up to see it for myself!

I think both ways have benefits...but I HATE dual zone setups where the passenger puts their fingers on the buttons and thinks that they can somehow have control over the temperature.

 

So i just noticed it goes up a couple hundred rpm? That’s kind of a lot. Not sure why why heat would do that. Need to try it myself next time I start it.

 

There are TONS of people with other vehicles asking the same thing, according to the Google.

I suspect it's a situation where there's just enough extra load to drop the voltage enough to in turn have the computer kick up the idle to keep the battery charged. How old is your battery?

 

AC systems usually default to being on with the defrost. However, it should also be noted a lot of AC compressors won't run below certain temperatures. I've never paid attention with my 4Runner, but every other vehicle I've owned (including my Tacoma) will not run the AC compressor below approximately 45°F even if you have it selected to be on and the light indicates it is running.

 

I tried it. No rpm change. OP said it wasn't cold enough (in the 20's) outside.

 

OP I noticed this too and not normal in my 52 years of life.....hot coolant is already circulating through the heater core and friggin turning the fan on does not add any load to anything! Well at least not enough of a electrical load on anything else I have ever owned.

AC is off or I would understand a compressor adding a load.

 

https://macsmobileairclimate.org/2014/09/17/blower-motor-draw/


it may not be a big draw, but it still is using energy.

 

If this were just because of the fan amperage draw then it would happen anytime, regardless of outside temp, it would also happen using the fan to blow cold air. I don't think this has anything to to with amps. I tried plugging in a phone to the charger as suggested and this does nothing. Turning on headlights also does nothing (as expected).

If I manually turn on the ac the idle revs do not really increase, I see a brief and subtle drop in rpm as the engine is loaded, then idle revs are back to about normal. It only happens when very cold although I don't know the exact temp, somewhere around 10 degrees F or lower, not sure. The truck might be reacting to outside air temp, cabin air temp, engine coolant temp or maybe more than one temp variable. When I first experienced this I assumed it was simply fast idling to heat up more quickly because it was very cold and the heater was calling for heat. This seemed simple but now I am wondering if any of you understand the computer logic that might be causing this OR the problem that my truck might have.

Battery is original 2020, yes it's 3 years old and the truck has done this high idle when cold and heater on since new.

 

Interesting, you have to be quite perceptive to notice this, i suspect that IF its jormal most people do not realize it is happening. What year and trim is your 4runner?

 

So, it's been doing this for 3-4 years and you're just asking about it now?

FWIW, batteries don't last very long in these things. I would get it tested just to see what kind of condition it's in. Most Auto parts stores will do this for free. Make sure you go to a place where they load test it (usually they will have you start the vehicle while the tester is attached).

 

If it's the battery then why only when heat is on? Fan on cold does nothing. Read the OP, the important details are all in that first post. I am not wasting time with the battery, unless I suspect battery. And yes, this has been happening for 3 years and I am asking now.

 

I didn't say it was the battery. I said you might want to get it checked just because they tend to crap out after 3-4 years on these things. See below from my post.

 

2023 SR. And yes I am hyper sensitive to all things mechanical.

Owning old stuff makes you a diagnostics expert......for real man!

 

It totally reminds me of a vacuum leak. Obviously it is not that but that is exactly what if "feels" like.

 

And IMO NO WAY a Japanese Panasonic battery lasts any less than 10 years. I would be shocked! I get 10 years out of off the shelf Interstate batteries.

My 4R is 6 months old with 6k miles on it and it has done this from day one.

 

Does yours have a Panasonic battery?

I don't think mine did.

My '03 had a Panasonic, and yes it did last forever. But, that wasn't the case at all in my '19. 3 years in I was getting weak starts and the battery tested borderline, so I just replaced it.

Good luck if you think you're getting 10 years out of your current 4runner. These newer ones seem to have more parasitic draw than the older ones.

Get ready to be shocked.

 

I'll watch and report back. Yes Panasonic.

 

Hopefully you have better luck than I did. I was surprised that mine was already crapping out when it did.

 

nobody is denying a blower motor requires energy…

 

@Thatbassguy my '19 is pretty much a twin of your 4Runner. I bought mine in September of 2019. Still on the original battery with no issues. One big difference is I don't have the cold temperatures that you do in the winter. Except for my Boise trips in January and February. My truck only has 40k mileage, so that means it sits a lot. Battery has been very good.

In reference to the OPs question, my thought was this: isn't there a cold start valve or solenoid something in the fuel injection system that adds an extra amount of fuel when really cold? Tody's fuel injection systems might not have this but years ago they did, maybe not Toyotas though.

 

Do you mean your 4runner idle speed increases when the engine is cold, outside temp is less about 10 degrees and the heater is turned on? What I described in post 1?

 

That’s gonna be my guess, a particular set of variables that happens at very cold temps, that trips a higher than normal idle for a faster warm up. A few hundred rpm increase is large, and seems very purposeful.

Next time we get a cold snap in my area I’ll try to remember to play around with the dials. Unfortunately, I’ll probably forget because it will probably be in the morning before my coffee has completely kicked in lol.

Do you live in the US or Canada? Block heater? Just asking because Canadian versions might have their own cold weather logic.

 

US, Wisco. no block heater

 

Yes sorry if I was not clear. I re-read post 1 and that is what is happening. Simply put, simply turning my fan on increases engine R's by a few hundred....turning fan off instantly lowers R's. I have not driven it enough to lock down specifics (it is my wifes.. I have a new Tacoma I just got last week and I am pretty sure I felt that do it also!) on outside temps etc. So it seems it is a Toyota thing...to me....at this point.

I do know it is enough to clearly feel and enough to make me push the brake a tiny tiny bit harder oif I am stopped at a light when it happens.....hence my comment about it reminding me of when I had a vacuum leak on a 4.0 Jeep.

 

Does the high idle happen in drive and after it’s warm too?