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Discussion Starter #1
Hello everyone, I recently purchased a 2000 Toyota Avalon XLS with 122,000 miles on it. The vehicle runs perfectly fine when the A/C is not running, however, when I do turn the A/C on, I notice minor tugging or jerking in the engine anywhere between 40 - 75 mph. The vehicle was not doing this the first few weeks that I drove it. No codes are showing and I had the local Toyota dealership and a friend's automotive shop take a look at it only to be told that it was not much of an issue and that it's normal for this vehicle to do this. It seems as if the tugging is occuring when the A/C compressor engages and disengages. Wondering if maybe its low on freon? I also noticed once when I was at a stop light that the car jerked forward as if it wanted to take off while my foot was on the brake. Any advice would help, thank you for your time.
 

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If Toyota and independent service techs say nothing is wrong, then it's just a guessing game over the internet. The compressor may be low on freon and it cycles more to maintain the selected temperature and you'll feel it at all speeds not just the range you mention. Does the AC cool adequately?
 

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Discussion Starter #6
The car idles at approx. 700-800 rpm. I am however going to check the freon level with my a/c guage. I know that compressors low on freon usually engage and disengage more ofter when freon is low. I just have never encountered this tugging when my other car has been low on freon before. That might just be it. I will get back to you guys, thanks for the advice :thumbsup:.
 

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Discussion Starter #7
I checked the A/C, the freon was borderline low. I added freon and drove the car around town for a bit. The cabin is now considerably cooler. I didn't notice anything unusual with the jerking except for the fact that I noticed the car sort of jump when I was at a stop light. I noticed the rmps slightly climb for a brief second and then all was fine. It's as if something is happenning with the idle, but yet only when the a/c is engaged. This is the second time the car has done this ??????. I am going to drive the car this weekend and will have a pretty good assessment in a day or two. Any suggestions with this idle issue and perhaps its linked to the jerking, I'll be in touch, thanks for the help :eek:
 

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I wonder if the jump you're experiencing is caused by the computer attempting to correct a low idle condition. If the a/c compressor drags for a moment, then releases just as idle is increased by the computer, wouldn't this cause a surge?
 

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Discussion Starter #9
Hello guys, I drove the car around this weekend. It appears as if the tugging and jerking was corrected by adding freon to the a/c :thumbsup: Thanks for the help!. Getting back to the jump or surge. The car did jump one more time this weekend when I was at a stop light. Yes, it seems as if the computer is attempting to correct the idle speed, so what if anything can I do. Is this something I should worry about or is it maybe a sensor or a solenoid? Hard to tell when no check engine light is on! Any suggestions, thanks for the advice I sincerely appreciate it! :eek:
 

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Discussion Starter #11
The car runs great, it only seems to have this minor idle issue when I run the a/c and not at every stop light :eek: What can this be?
 

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The engine control module learns how to operate the idle air control motor based on past running conditions. It is possible that the adaptive memory needs to be cleared and the idle strategy relearned.
 

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Discussion Starter #13
So how can I clear the adaptive memory and reset the idle. Is this simple or would I need to take it in to a shop?
 

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Clear adaptive memory

Sometimes unhooking battery and completely discharging the electrical system will work, sometimes it requires them to be cleared with a scan tool. I am unsure if the battery unhook will work on the avalon as I have access to a mastertech scan tool and I use that. To try the battery unhook, you will want to unhook the battery then turn on the key and headlights and step on the brake pedal a few times. let car sit for 10 minutes and hit the brake pedal a few more times. Turn headlamps back off and key off then unhook battery. This may sound excessive, but you are trying to discharge all capacitors in the modules - by turning on electrical devices with the battery unhooked you are trying to give them a path to ground to discharge. Some people will say to touch the battery terminals together, but I do not recommend this - while it may not hurt the toyota, it is not good practice as it provides a dead short rather than a loaded circuit. this can lead to voltage spikes which can damage electronics in certain cars - I like to stick to good practices as it keeps accidents to a minimum.
Of course - the idle is adaptive. If the idle fluctuation was from the A/C being low on charge, the car will learn (in due time) and correct itself - this may take a while.
 

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correction to reply

Please be advised of this correction: "Turn headlamps back off and key off then unhook battery." THIS SHOULD READ....then hook battery back up.
The important part here is that you want all elecrical loads turned OFF when hooking the battery back up :). Let us know if battery unhook works. Also - when you do this, if it clears the adaptives, it will clear ALL of the adaptive. This means that the vehicle will shift differently and may actually run differently. These cars learns how the driver want them. they will change when and how aggressive the cam advance is, when and how aggressive the shift patterns are, idle properties, etc. you will be clearing all of those if the battery unhook works. you will need to drive the car as you intend to drive it (both in town and on the freeway) while it relearns everything. This could take up to 100 miles to get squared away, but in my experience it does it quicker than that. SO you know - nearly all new cars are this way.
 
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