I have a 2005 Toyota Vitz with a 1KR-FE engine. When idling, there is a rough idle from time to time when the car is in Park, Neutral or when stopping in traffic, with vibrations shaking the car. The problem worsens when the A/C is switched on sometimes. What could be the problem? Car has been regularly serviced and fuel is 98RON. the issue has been going on since I bought the car second hand. No check engine lights. Thanks.

  • Engine mounts? I have had non-severe variation of the problem on all cars that I have had for a long amount of time. I believe it's caused by engine mounts. Personally, I wouldn't bother about the problem unless it's really severe.
    – juhist
    Feb 24, 2017 at 16:16
  • Welcome to the site. We will try to help if you give us a little more information. When was the last time it was serviced? Are there any lights (check engine) or warnings on? How long has this issue been going on? What is the quality of the gasoline you are buying? Please add extra details by using the edit feature.
    – CharlieRB
    Feb 24, 2017 at 16:24
  • check rubber engine mounts, change the garage where you buy fuel.
    – user26112
    Feb 24, 2017 at 18:15
  • No check light or any other lights.
    – Madhana
    Feb 26, 2017 at 9:53
  • Car has been serviced on time and fuel is 98 RON available in any irish service station. the issue has been going on since I bought it.
    – Madhana
    Feb 26, 2017 at 10:20

1 Answer 1


Let's assume you have already checked for small vacuum leaks in the rubber tubing on the intake manifold and replaced the PCV valve (if applicable) . . .

I had the same problem on three different cars (two late-model Mercedes-Benz). The problem were due to dirty fuel injectors, spark plugs, intake valve stems, idle air control valve and flow ports, and other deposits. Cars are particularly susceptible to deposits in cold climates, like Ireland.

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