Rough idle with AC

Got a 2019 4.6 crewmax, 6500 miles, now that it has gotten warm i noticed when the AC is on and im at idle when the ac clutch engages my RPMs go to 600 rpms, usually my rpms stay between the 400 and 600 lines so i guess at 500. When the clutch engages it idles rough, i can feel the vibration through the brake pedal. Sometimes when the ac clutch engages it actually nudges the truck forward a bit if i dont have the brake pressed firm. If i turn the ac off, ir when the clutch disengages its smooth no issues..... anyone having this issue, any idea what it could be??? im gonna have the dealer check it out at 10k service but figured i would ask to see if anyone has experienced this or if this is normal.

 

Not normal. I have never noticed it on my 2017 4.6L, but it sounds like the AC controls automatically boost the idle speed to compensate for the AC compressor load. The "idle-up" feature has been around for a long time on smaller Toyota engines, but I did not know it was necessary on the V8s. The rough idle is not necessarily related to the increased idle speed, but it may indicate a vacuum leak that is associated with the increased idle speed. I have no idea how an idle-up function would be accomplished now, but it used to done with a vacuum switching valve.

Let the dealer check it out for you.

 

My 2018 4.6 is very smooth at idle

 

Thanks four your input fellas... i will definitely update once i take it to the dealer, with my luck it wont do it when its in there.... anyhow, got 100k mile warranty on everything so i figured if it's not supposed to be this way something will eventually give.

 

I have to check this with my Tundra but with my other DD, if I turn the ac on at idle, the rpm goes up by 200 and If my foot is lightly on the brake, the car inches forward due to higher rpm. So this seems to be normal.

As far as vibration, etc. The cause could be the compressor or the belt. Since yours is 2019 it's not very likely that the compressor is failing.

Also I am curious now to check my idle rpm. I think without ac, mine idles at 600-700 rpm so your 400-600 seems to be lower than my '16.

 

Have the dealer check or possibly clean and or replace the idle air control valve . Should be well under warranty.

 

Could be the amplifier sending improper signals if the engagement of the compressor is harsh

 

It runs smoth without the AC or when the clutch/compressor disengages, as long as its not engaged it smooth even while blowing air.

 

With the ac off try and hold the truck at around 800 rpm, and see if its rough. Also the idle up is normal so the ac doesn't warm up at a stop light

 

Idle up is normal to neutralize engine load. Cooling fans function is for air flow over the condensor at idle, not engine idle speed.

 

Modern vehicles don't have to equalize load, the idle up is to 1, increase rpm of ac compressor for better efficiency 2, ramp up speed of cooling fan for more airflow when stopped.

 

I checked mine today.
'16 V8 5.7 gas

My reading is from the car tach. I should use my scangauge to get the exact rpm but I didn't have it with me.

idle rpm is 700 almost 750
This is after car warmed up and same after 40 min drive ...

at idle if I turn the ac on, rpm dips a little for a couple of seconds then back to 700-750. Same as idle with no ac.

When I turn ac off, rpm jumps a little for couple of seconds and then back to 700-750

Basically it holds 700-750 no matter what. Also no vibration or anything like that. I heard a little noise initially when compressor was engaged but it went away.

You car is idling at 400-600
Maybe that's a new thing to save fuel? idk

Others with newer models can comment about their idle rpm.

not saying that's your problem but curious why you are idling @500 and I'm @700.

 

Idle-up on engagement of the compressor clutch was critical to AC performance on a 22RE.

For years, I drove my 86 4Runner without air conditioning, fearing the expense of compressor replacement and recharge with heavily regulated R12 refrigerant. When the compressor kicked on, it would drag the idle speed down to the point where it was near stalling. I finally diagnosed it was the idle-up solenoid. Once I found a used Lexus solenoid (not available as a new part), and retrofitted my 4Runner mounting bracket, the idle-up worked like it should. After that, the AC performed fine without a recharge.

 

Your idle should increase when the compressor kicks on, that is normal operation, it's just not to neutralize engine load, it's to increase the cooling capability while the vehicle is stopped.

 

Do you have reading material for this theory?

 

https://www.vintageair.com/basic-auto-air-conditioning-compressor-facts/

This is a very good read on modern vehicle ac compressors

 

So did some quick reading,
I must have missed the obvious where it states that the increase of 100-200rpms increases the cooling capability at idle. I'll take a better look later.

 

Thanks for the replies everyone. Once it goes in for 10k service i will have them look at it and post back. It will only get hotter here in GA so it will drive me nuts as i drive a ton, hit 7000+ this morning on the way to work since my OP i was at 6500.

 

Did you ever get an answer on this. Mine does the same. I notice it more now with cooler weather as the ac short cycles more. I’ve even tested it while on a gentle acceleration or holding a steady speed. When the ac engages I get an increase in rpm, whether at idle (in drive), accelerating or holding a speed. I can understand increasing idle while stopped but I’ve noticed a slight bump in rpm when accelerating from a stop when the compressor kicks on. With ac off I get the same idle up situation when I turn on the headlamps from auto to on, in all the situations described above. I don’t really mind it but when I sit at a stop light the truck definitely surges forward if I don’t have the brake firmly pressed. Thoughts anyone?

 

I know I'm old school but what you describe is usually a vacuum leak. A vacuum leak will cause a lean condition (a scan tool with live data should show this) can't handle much engine load (like your AC) without the idle dropping a lot.

 

I had a rodent get in and chew some
Insulation and try to make a home under the intake manifold. I cleaned it all out and haven’t had any activity in months and checked the hoses I can see with no apparent leaks. Are there vacuum lines that run under the intake manifold or under and in back that aren’t easily visible that could have suffered rodent damage? Lots of work to take the manifold off for nothing.