2005 Toyota Corolla Vibrates when AC is on at low speeds

Tiny
VINDHA
  • MEMBER
  • 2005 TOYOTA COROLLA
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 102,000 MILES
Hi,

I recently bought a Corolla AT [ done 102,000 kms] that seems to drive noiseles and vibrationless except when the a/c is on at low speeds [ 0-5 Km/hr speeds] when the vibration and noise is quite pronounced, and this noise and vibration both build up for a while and then subside. At the height of the buildup, the vibration is quite high. This is quite pronounced in D mode. In N, one can still feel the vibration but is lesser. The Toyota workshop suggested changing the engine mounting, and they have changed a part called "Insulation, Eng Mounting, Fr" - however, this hasnt solved the problem at all. I checked with a third party mechanic and he suggested the problem still lies with the engine mount.

My questions are two fold

1. Is the part changed by the toyota workshop the complete engine mounting, or a part of it? If its only sub-part of the mount system, should I go ahead and change the entire mounting?

2. Is the problem related to the a/c system instead? Should I get the a/c clutch, compressor etc checked instead?

3. I also read on this website that this problem could be related to engine harmonic balancer or the AT Flex plate - should I check these too?

Thanks a ton! I am so irritated with this problem, that I am thinking of selling the car, which I really cant afford to right now. Hence, your help to identify the problem will be really appreciated:)
Please help!

Cheers.
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Tuesday, August 3rd, 2010 AT 8:02 AM

12 Replies

Tiny
DR. HAGERTY
  • MEMBER
Thank you for your donation. It seems that your issue is the A/C system. The statement that the engine mounts are somehow involved seems unlikely due to the lack of vibration when the A/C is not on. The A/C compressor should not transmit vibration enough to cause you to be aware of it, I suspect the pump is the culprit here. I also want to invite my associates here in the forum to add whatever might help you with this issue, anyone else seen this before?
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Tuesday, August 3rd, 2010 AT 9:51 AM
Tiny
VINDHA
  • MEMBER
Thanks Dr Hagerty. I also came to the same conclusion, however, the vibration is not perceptible when the a/c is on at speeds above 20km/hr. Does this mean there could be another possible source of vibration[ that kicks in only at lower speeds]? Would be good to know your thoughts on that.
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Wednesday, August 4th, 2010 AT 5:58 AM
Tiny
DR. HAGERTY
  • MEMBER
My strength is BMW cars and when this happens on a BMW it can be mitigated by changing the engine speed, so Toyota cars can be the same in as much as the systems operate in a very similar fashion. If the vibration only occurs when the A/C is on, and subsides when the speed is changed, it can indicate that vibration cancelation from the mounts may not be at its best and changing them might help, but A/C compressors aren't supposed to vibrate.
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Friday, August 6th, 2010 AT 1:27 PM
Tiny
VINDHA
  • MEMBER
I went to a third-party [ non - Toyota ] mechanic today and he said the problem is that of low engine idling speed. He said that my car was idling at 600 rpm when the a/c was on[ and 800rpm when the a/c is off], which he said was too low. He increased the engine idling speed mechanically, and it now idles at around 1000 rpm without a/c and 750-800rpm with a/c. This has solved the problem to a great extent. He suggested that increasing the idling speed further could completely solve the issue, but advised against the same since it could increase gas consumption by a lot.

It would be great if you could validate what he is saying and what he has done. Is 800 rpm the right idling speed with a/c on?
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Tuesday, August 17th, 2010 AT 11:25 AM
Tiny
DR. HAGERTY
  • MEMBER
That sounds quite reasonable to me, raising the idle is solving the issue and I too do not think more is better here. I have a concern that there might be something may be at fault in the idle control, compensation of idle speed due to the A/C should be taken care of automatically, at least it seems so to me. A 2005 Toyota is fuel injected and should have idle compensation, however I am not a Toyota expert, I will transmit this thread through the moderators forum, please stand by, Dr. Hagerty.
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Tuesday, August 17th, 2010 AT 9:49 PM
Tiny
BLUELIGHTNIN6
  • EXPERT
Looks like I'm going to have to agree with the third-party mechanic and the Doc here as far as not speeding up the idle any more. It seems this is only a temporary fix to a bigger problem. The idle speed should be around 750 RPM whether A/C is on or off, give or take 50 RPM. If it's now idling at 1,000 RPM with A/C off, that is a bit high and is already consuming more fuel than is needed as well as stressing engine more than is needed. I did look through the technical service bulletins and recalls for this Toyota and none relate to this issue, so it is apparently not common. One thing comes to mind is if the compressor is low on freon it may turn on and off continously, this would definitely throw off the idle of the engine so that is something that could be checked out.
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Tuesday, August 17th, 2010 AT 10:55 PM
Tiny
KHLOW2008
  • EXPERT
There are a two fold problem here:

1. The ldling speed when A/C is turned on is too low. When turning the A/C on or off changes the idling speed, the throttle body and IAC are probably dirty resulting in air flow restriction. This would affect the idling speed.

Try cleaning the inner port of the throttle body and IAC, especially between the throttle plate and retest if the idling speed stabilises when the A/C is turned off.

2. Vibrations are most likely due to the engine mounts.

There are 4 engine mounts and the one replaced is the front, which is not a major part of the engine mount system.

The engine mount most likey to result in vibrations would be the one at rear or right of engine compartment.

The idling speed is non adjustable and what did the mechanic do to increase it?
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Wednesday, August 18th, 2010 AT 10:43 AM
Tiny
VINDHA
  • MEMBER
Thanks Dr Hagerty, bluelightnin6 and KHLow2008 for your advice!

Bluelightnin6, yes - I will get the freon levels checked, and the a/c compressor checked as well, as per Dr Hegerty's suggestion.

KHLow2008, thanks a ton for mentioning the difference between the front and rear engine mount - maybe I need to investigate this as well. The throttle body was cleaned when the engine mount was changed - here I have a question - is the IAC a part of the throttle body?[ The Toyota service center mentioned this], or do I need to ask them to specifically clean the IAC.

The third party mechanic changed the idle speed by changing some setting near the engine under the hood. I was actually surprised because the toyota service center specifically mentioned that the idle speed cannot be adjusted. I understand the point about stressing the engine out and will probably get this back to the factory setting.

I have scheduled an appointment with the toyota service station for next Thursday[ 19th] and plan to request the following [ let me know if I need to rephrase anything here]

- Check a/c freon level and refill if need be
- Check a/c compressor pump for any vibrations
- Check if ECM is providing a/c compensation at idle
- Check and replace rear engine mounts.

Thanks a ton - you have been of great help!
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Thursday, August 19th, 2010 AT 8:54 AM
Tiny
KHLOW2008
  • EXPERT
The IAC is a separate component attached to the throttle body and the dealer would sell it to you as part of the throttle body.

Actually there is no repair manual for cleaning the IAC and the trick was learnt by people on the job. When cleaning the IAC, the throttle body has to be removed.

As I suspected, the mechanic must have tampered with the factory settings for the throttle plate to open it more than standard. The throttle stop screw is set at the factory and should not be tampered with. It is not easy to get it back to factory specs without the aid of expensive machines, which are not found anywhere except in the manufacturing factory. An experienced mechanic should be able to get it back for you but no guarantee it to be perfect.

Tampering with the idlng speed would still result in it being erratic so it actually does not help.

You don't actually stress the engine out by adjusting the throttle stop screw but it would affect idling and rpm fluctuations.

The A/C compressor should not cause any vibrations. If they do, there would be other abnormal noises as well. Any vibrations from the compressor would more likely to be the mounting bolts for holding it and its base bracket. Check them for proper torquing.
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Thursday, August 19th, 2010 AT 9:18 AM
Tiny
VINDHA
  • MEMBER
Hi everyone,

Thanks a ton for all your advice. The car came back from the Toyota service station and the vibrations have more or less completely disappeared!

To give you the complete story, here is what the service advisor told me they observed as reasons for the vibration once they inspected the car:

a) Engine mounts were cracked up and had to be replaced
b) A part called the drive shaft boot was found to be causing some noise and had to be replaced
c) Something called the engine shield was broken and had to be replaced
c) There was oil leakage from a cylinder and hence a gasket had to be replaced.

They went ahead with all of the above. The engine shield replacement was not available in stock and hence they repaired it[ re-welded it? ]

Here are my observations after driving the car around for a couple of days after it came back:

1. Close to zero vibrations now from the engine:) Though I do sometimes feel while accelerating that there is something that can be felt near the drive shaft [ that would be near my left leg in the driving position?]

2. A/c seems to be idling smoothly when in N or P. However, when in D mode and not in motion [ say at a stop signal], there is still some periodic variations in idling that one can feel both as sound and vibration

3. Idling speed seems to be hovering around 850.

I do have a concern here: Is the oil leakage from the cylinder and / or the drive shaft boot replacement a cause of concern? I just need to know if there is a possibility of long term engine damage that may have already occurred or I need to watch out for. The service center guys told me they had done a complete check on the engine and found it to be completely ok.

Thanks a ton once again, and would be great to know your thoughts on the above solution from the service center.

Cheers!
Aravind
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Saturday, September 4th, 2010 AT 2:24 AM
Tiny
MERLIN2021
  • EXPERT
If after all the repairs you still have a vibration, it could be a simple matter of one of the A/C hoses touching another part, or rubbing on the body someplace, check the hoses. Cracked CV boots dont usually allow dirt into the joint, but split boots do, it depends how bad the boot was? If the oil leak is fixed, and the engine did not run low on oil, no lasting damage will occur.
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Saturday, September 4th, 2010 AT 11:12 AM
Tiny
HMAC300
  • EXPERT
Everyone else has thrown an answer so i'll give mine. I ran into this same problem many years ago on a Cadillac. Back then they used 2 belts to run the compressor and the compressor was mounted to the engine so all the vibration was felt throughout the car. However the fix dealt with belt tension and matched belts. Of course that may not be the case nowadays with the 2 belts. But I would suggest 2 things, first test the belt with a tension gauge if any mechanic stil have oneI do lol- Because the tensioner may not be holding the correct tension when the correct tension when the a/c is applied. AFteer all the tension shold be about 100# or so for everything even with an automatic tensioner or manual one. The i'd have the flex plate checked for cracks as that can happen and will let the torque converter flop around or at least wobble and not do the trans oil pump do any good either. Thats my two cents.
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Sunday, October 3rd, 2010 AT 1:19 PM

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