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I replaced the PCV valve of my Toyota Vitz 2007 some time back, due to oil level reducing. After I got the car back from the mechanic, it had this weird behavior of making a sudden jerk after five or six seconds when car is stopped in traffic. Also, it jerked when shifted to drive gear from parking gear. Jerk is not that violent and it does not make the stopped car actually move forward. Its like the car is trying to jump forward.

After about a week or so, this got automatically fixed.

I repaired the car again from the same mechanic, this time a soldering job of an electrical cable which supplies power to one of the spark plugs. After I got the car back, it showed similar jerking behavior. Now its been three or four days and jerking has got resolved to some extent, but still car does not feel the same as it previously was.

(About the soldering job, two wires which supplied power to a spark coil had been damaged at the point the wires connect to the socket at spark coil. Mechanic told me that its hard to find spare sockets so he soldered the wires. But I don't think the cause of jerking is related to this, because the same behavior occurred previously too, when there was nothing wrong with the wires)

I asked the mechanic whether he did anything else other than soldering the cables, but he said no. But, he should have disconnected the battery, because the time in the dashboard clock was incorrect when I got the car back.

Few more information:

  • My car had been idling roughly for some time now.
  • Earlier the gas mileage was about 12.5km/l. But from few months back, it has droped to about 10km/l.
  • After the repair, when the car is at a stop, it does not properly go forward when I release the break (without stepping on the gas paddle).

What could be the reason for this jerking behavior?

  • Could you please better describe what you mean by "jerking"? If there was a problem with the sparkplug wires, they should be replaced, not soldered (unless you are talking about an issue with the coil associated with the spark plug). If a spark plug lead was actually fixed this way, it might be causing you issues. Battery disconnect is fairly common practice when working on anything in a vehicle, just for safety sake, so no worries there. – Pᴀᴜʟsᴛᴇʀ2 Jun 28 '15 at 10:31
  • @Paulster2 Updated the question. Please check – Lahiru Chandima Jun 28 '15 at 10:45
  • The job he did now makes sense and is proper. Surging sounds more correct than jerking, but that is more interpretation. I'd suggest there is an issue with the Idle Air Control (IAC) valve, but I'm not even sure if it has one. What year is your car (they started making the Vitz/Yaris in 1998)? – Pᴀᴜʟsᴛᴇʀ2 Jun 28 '15 at 10:57
  • Its 2007 model. – Lahiru Chandima Jun 28 '15 at 11:02
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It turned out to be a result of disconnecting the battery from the vehicle. When the battery is disconnected, the ECU forgets what it has self learned about when to switch gears, how much to open the throttle valve, etc.

After few days driving, when the ECU re-learned, the problem went away.

I had to disconnect the battery again recently, and the problem occurred again. Again after few days driving, it got back to normal.

  • You may want to invest in a memory saver tool if you ever have to disconnect your battery again. – Ben Feb 12 '16 at 20:39
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    You can award yourself the answer to this and will get a badge for answering your own question. :-) – DucatiKiller Feb 20 '16 at 22:05

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