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My problem is that sometimes when my Astra G tdi 1.7 2002 is idling (is not in gear) the RPM will go to 5000-6000 with out me stepping on the gas pedal. The engine accelerates on its own while idling. I tried reading online and found a post that this could be because of the Idle Air Control Valve. I told this to my mechanic and he told me that my car and diesel engines don't have Idle Air Control Valve. My question is first do diesel engines have an Idle Air Control Valve and where can I locate it on my Astra G?

This is an image of the engine:

enter image description here

BTW, the mechanic has no idea what the problem is.

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    I cannot tell you for sure, but it doesn't look like it has one. It is not listed as a part at a couple of different parts outlets in the UK. Two things surprise me about what you are saying ... That is revving pretty high for a diesel engine (heck, that's pretty high for a petrol engine), and secondly, it sounds very close to being a runaway. A runaway is just what it sounds like, when a diesel engine speeds up on its own and goes to redline or has high as it can go and stays there. Maybe yours has a shutdown mechanism which gets it to idle down. I don't really know, though.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Mar 26, 2015 at 22:51
  • Thanks for your answer, so I also did some research this this days, so it turns out that this there is no part like this in a diesel car. And there is a new moment, the car started doing this wile driving, but the RPM aren't that high probably they go to 3000-4000. And the red line starts from 6000 on from what i can remember.
    – user1796624
    Commented Apr 1, 2015 at 16:26

3 Answers 3

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Diesel not have idle control valve as there is no concept of throttling and therefore no throttle pressure sensor

One of the possibility could be a bad Acceleration pedal sensor which can give a wrong input to ECU.

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  • Thanks for your answer, about the idle control valve, About the pedal sensor i have changed the pedal and i get the exact same thing.
    – user1796624
    Commented Jun 2, 2015 at 14:55
  • Are you getting any fault codes when you check with scanner?. Since the engine RPM is also pretty high, there could also be some issues with ECU. Probably you can take the vehicle to workshop to check if the ECU can be reflashed. Sometimes there could be errors with the software for which updates may be available!!!
    – knocksAndMisfires
    Commented Jun 2, 2015 at 15:56
  • Thanks for the answer, Yes they are suspecting the ECU and they want to change the entire unit.
    – user1796624
    Commented Jun 2, 2015 at 16:15
  • Try updating the software before replacing it. That would turn out cheaper!!!
    – knocksAndMisfires
    Commented Jun 2, 2015 at 16:24
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    Reflashing I don't know the details. for updating the software, you need a scanner!!! Best thing is to visit a Authorised workshop or IAM workshop with a tester that has pass through capabilities
    – knocksAndMisfires
    Commented Jun 2, 2015 at 16:29
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it turned out that the car was tuned and it had some extra electronic that was connected to the computer and the fuel pump. This wasn't a native part of the car and it was hidden. We founded after expecting the electric installation and searching for problems there. After removing it there are no problems and the car runs great. Ill try to post pictures from the model later. Thanks all

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Two things to check:

  1. The TPS (throttle position sensor) or a bad ground to that sensor.

  2. It could also be your engine temperature sensor which I believe is located near the thermostat on that vehicle. With colder engine temps, the computer will increase fuel. If your sensor is giving off erratic readings that could cause it to jump in RPMs like that

Best thing would be to hook it up to a scanner and check things like the TPS position, pull codes etc.

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  • Thanks for your answer, so i have been noticing that the temperature sensor isn't working that great it seams that the car isn't going above 80 C , or really goes above 80, but I also drive on quite low rpm 1500 - 1800 . Is there a method that I can check if the temperature sensor is ok? Also a sub question is there a way to clean the cylinder/clips, one mechanics suggested that i use a additive for the fuel and try to drive on high rpm in order to clean the fuel system and the cylinder
    – user1796624
    Commented Jun 2, 2015 at 14:54

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