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2011 Diesel 2L 120kw LTZ - Strange idle RPM issue

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What troubles me is another problem:

  • Drive the car for a while
  • Press clutch and break (for example on red light, doesn't need to be fast breaking)
  • Engine RPM will be dropping below Idle and jumping up and down between 500-900
  • This will continue until
    • A: Car stops moving (brake can still be pressed)
    • or B: Releasing the brake for longer time while car is still moving

  • Then RPM is stable at idle (pressing the brake when car not moving at idle = IDLE rpm is stable)

At first i thought it is just RPM sensor or "gauge/display" acting up because engine doesn't produce vibrations or sound that would suggest it is close to stalling. But then driving at night i noticed when this is happening the lights intensity is going up and down together with RPMs.

Really baffled by this. I mean it never ever let the engine stall and if not for the "blinking lights" issue i wouldn't even chase the issue.

Another (possibly related?) issue is sometimes current L/100km consumption meter is showing really high consumption and at the same time not showing 0 consumption when going downhill with gear engaged and foot off the throttle. This is however not bothering me so much right now just writing it as it may be related.

What is disappointing is attitude of local GM (Opel/chevy) attitude: I was at GM service here and they told me Cruze in general have problems with keeping idle rpms. It seems like they didn't even want to hear out the details about the problem. As soon as i told the "Idle rpm" they didn't even listen more just kept the it's Cruze just live with it attitude.

Thanks for help
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· Premium Member
4,647 Posts
I posted a reply to your other thread on this. Possible negative battery cable causing electrical issues. I've not heard of an idle issue on the US diesels.

· Premium Member
4,647 Posts
By that i guess you mean the issue mentioned by sticky thread about Negative cable connection on battery? I will check that tomorrow morning together with the tightness of the air intake stuff (I have read that is common issue somewhere else on this forum). Maybe hit it with Dremel a little bit if i see any signs of rust.

I tried quite a lot to diagnose the issue by logic (although with my limited knowledge about cars) and couldn't pinpoint what causes the issue (like why is it sometimes working and sometimes not...).

I was thinking about vacuum leak from break system - i ruled that out because RPMs hold steady idle if car is not moving and i apply break.
Another thing i noticed - when i break with engine and press clutch when RPMs are getting lower -> issue happens it will be RPMs will be going up and down, up and down until car stops. However if i just press the clutch and release brake RPMs will drop below idle return back to idle in 1/2seconds and after that if i break it holds idle RPMs perfectly.

This leads me to belief it may be some sensor/SW issue (but that is my imagination coming from me being SW guy working on similar systems... not automotive but lots of sensors, servos, stepper drives, vacuum/pressurized air, lasers controlled by computer... We call it Mechatronics here).
It seems almost like the SW doesn't know clutch has been pressed? I have cheap USB/OBD interface from ebay... didn't try it yet with Cruze. Do you know if it is possible to log this values with free SW (RPMs, Clutch pedal position, Brake pedal position, Throttle pedal position etc)?
Yes it's the one about the negative battery cable extended warranty. it solved some random electrical issues on mine.

To answer your other question, I have a Scangauge II to monitor tings on the vehicle. I am not sure if there are any free apps out there that would work, however. Others may have more info on that.
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