My Toyota Vitz 2007 idles roughly when AC is on. If AC is turned off, the idle becomes much smoother.

This vibration is more visible if I suddenly stop in traffic. As soon as I stop, several rough vibrations occur and then it becomes smoother.

I got the vehicle serviced: cleaned the fuel filter, replaced Air and AC filters, replaced engine oil. But the problem hasn't got resolved.

What could be the reason for ths?

  • How many miles on the vehicle? Dec 13, 2015 at 13:37
  • @Paulster2, 86000 km.
    – Softcode
    Dec 13, 2015 at 13:41
  • There is a thing which causes the engine to idle up when the AC is turned on ... it seems this isn't working correctly. Your engine gets dragged down a little bit and causes the rough idle. I don't know what this is called exactly. Maybe someone else will have an exact answer for you. Dec 13, 2015 at 19:39
  • Did the issue come about suddenly?
    – Zaid
    Dec 13, 2015 at 21:42
  • @Zaid The car displayed rough idling for a long time and became more visible gradually over time. But it kind of got sever lately.
    – Softcode
    Dec 14, 2015 at 1:00

5 Answers 5


The symptoms are consistent with deposits in the throttle body. There are other potential causes. These deposits accrue in the intake manifold over time. They build faster with short trips and low quality fuels. Inspection and cleaning of the throttle body would be first thing to look at for this symptom. This engine is equipped with a computer controlled throttle system. It is designed to adjust its opening to keep the idle speed close to 700 rpm regardless of engine load. If to much dirt collects around the throttle blade the system can get beyond the limits of the systems ability to adjust idle speed with the extra load of the air conditioning.

To clean the throttle use a soft cleaning cloth soaked in a solvent. Open the throttle blade carefully. Clean the throttle blade and the surrounding bore. Do not scrub, let the solvent do the work, no scratches are allowed on the polished bore.

After cleaning start the engine and let it idle for at least 20 minutes while the system learns it's new throttle position. This vehicle should relearn on its own. It may need to be revved up and put in gear several times during the learing time. Note that other designs require tools and procedures to perform the throttle system relearn.


  • These geared blades are very strong and can damage body parts if they activate during cleaning, Make sure the vehicle key is away from the vehicle. Open them slowly and carefully. We use shotgun bore cleaning swabs so we do not have to insert fingers into the blade area
  • Do not spray solvents into the bore and intake, just soak the cloth.
  • Do not use metal tools for cleaning, it is easy to cause damage and these units are expensive.

If indicated, have cleaning done by an experienced technician if at all unsure since it is possible to get injured or damage a very expensive part.

  • Thanks for the answer. I will clean the throttle and see whether it resolves the problem.
    – Softcode
    Dec 14, 2015 at 0:55
  • @fredwilson Nice answer again. Dec 14, 2015 at 1:00
  • @fredwilson Can you please tell me whether it is necessary to trigger the re-learn in some way after cleaning the throttle body? I have asked a separate question for it. mechanics.stackexchange.com/q/23407/11037
    – Softcode
    Dec 15, 2015 at 1:25
  • Cleaned the throttle body and disconnected the battery for some time. After engine re-learned, vibration has reduced significantly.
    – Softcode
    Jan 19, 2016 at 2:41
  • I'm glad you got it worked out. In addition to the dirty throttle body, an idle control air valve could cause this issue. The idle air control valve adjusts how much air is bypassing the throttle plate, increasing air flow when the AC compressor clutch actuates to help the engine stay at idle speed when under the extra load.
    – David Sain
    Feb 2, 2019 at 5:47

Had the same issue on my Toyota Matrix turned out I had several vacuum leaks replaced the pcv valve and hose; and both the intake manifold gasket, as well cleaned the throttle body and put a new gasket and solved the issue. Hope this helps


I have an 03 camry with a fly by wire throttle body. The TPS and throttle motor needs replacing (all one unit). I just replaced most of the AC system and had it charged yesterday. There was already a problem with low and rough idle. I knew I would have a problem with the idle after I got the AC working. At rest the idle is at 14 to 16 % (engine not running.) Should be at zero, 1 or 2 and if over 5% has to be replaced. The computer is constantly trying to compensate. I've read lots of post and new throttle body's fixed it. However if you have an independent TPS you may be able to adjust it, or replace it. If you have performance mods you'll figure it out.


My answer is replacing your idle air control valve and oxygen sensor. Of course get the throttle body clean by with a throttle body cleaner or carburetor cleaner. Also check air filter makesure it's clean or new. But the really answer is the iac valve and oxygen sensor.


ac system not charged enough, dirty ac compressor and condenser, compressor broken, leak. alternator could be dying. sometimes the battery isn't charged enough and the car doesn't work properly.pulley, belt. could be anything spin the wheel

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .