# Rough idle?



## ProDigit (Aug 31, 2015)

I got a 2011 Cruze Eco 1.4t, with 50k miles on, everything stock, save for the tires, and transmission oil change.
Going for brake pads soon as well.

Anyway, it runs mostly fine, save for idle rpm occasionally drops below the standard 800rpm.
When it does, it's like the engine is choking, and trying to stay alive. (Ah, ah ah, ah, staying alive, staying alive)...

If I press the accelerator oh-so-slightly, and Rpm rises above 800, it runs smooth again.

I haven't found the cause yet, but wonder if this is common?
I'm thinking to change the air filter , and perhaps check the spark plugs.

Any other suggestions?


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## jblackburn (Apr 14, 2012)

If it happens at 1/4 on the temp gauge as the car is warming up, it is 100% normal. They do some weird valve timing stuff, I suspect to emulate EGR, when in the warmup stage. Feels like it's chugging.

If it happens when fully warmed up, and you feel like the idle is surging a bit, look for a vacuum leak. If the AC compressor is on and idle is holding steady, it is again, normal - it takes a lot from a tiny engine to run the compressor.


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## Chevy_Country (Oct 16, 2015)

My 2011 ltz 1.4t does this at idle too, only gets worse when an electrical load has been put on it, or ac compressor is on, and only gets better, like you said, when giving a little throttle.

I noticed a little difference when changing spark plugs, enough to convince me, that's just how the car runs, but I'd be interested to see if there's a "fix" 

11 Cruze LTZ 1.4T
04 Ranger XLT 4.0 4x4


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## ProDigit (Aug 31, 2015)

If the AC is on, the car actually increases idle RPM.. sometimes...

I have to investigate more, as I don't really know when it happens. I only noticed it a few times.

Any of you changed the air filter, and at how many miles?


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## jblackburn (Apr 14, 2012)

ProDigit said:


> If the AC is on, the car actually increases idle RPM.. sometimes...
> 
> I have to investigate more, as I don't really know when it happens. I only noticed it a few times.
> 
> Any of you changed the air filter, and at how many miles?


45K/4 years for me. Wasn't that dirty besides the foam on the bottom of it. No noticeable change after.

I might look into the spark plug boots and make sure all the springs are straight and nothing's corroded in there. That can make an idle difference.


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## Chevy_Country (Oct 16, 2015)

ProDigit said:


> If the AC is on, the car actually increases idle RPM.. sometimes...
> 
> I have to investigate more, as I don't really know when it happens. I only noticed it a few times.
> 
> Any of you changed the air filter, and at how many miles?


Changes my filter at 40k, like jblackburn said, I had no note cable difference besides knowing it was done

11 Cruze LTZ 1.4T
04 Ranger XLT 4.0 4x4


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## AzSandSlinger (Sep 10, 2015)

Clean your MAF sensor and your Air filter. I've seen this issue with worn Intake Manifold Timing Valves a well. Though that will usually throw a CEL.

I tossed a K&N in around 25k and clean it every oil change. The stocker was rough at that mileage for me.


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## ProDigit (Aug 31, 2015)

Well, the battery is brand new. Not sure about changing the sparkies yet.
Turns out that the problem solved itself with warmer weather.
It could be a combination of fuel and outside temps. It would be a good idea to have an additional jet in the carburetor to manually choke/enrich the mixture for optimal idling, as the ECU doesn't do a good job.
Perhaps it's running lean, and unburned fuel trips the CO2 sensor into thinking it's running way too Rich?

Anyway, now I know how to solve it.
Next time it happens, I just have to warm up earth first.


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## Merc6 (Jun 8, 2013)

ProDigit said:


> If the AC is on, the car actually increases idle RPM.. sometimes...
> 
> I have to investigate more, as I don't really know when it happens. I only noticed it a few times.
> 
> Any of you changed the air filter, and at how many miles?



Depends on the settings. The compressor is variable so if you aren't on the blue dot to the left of the temp knob it won't go full power. 

Another thing to take note is the Gen 1 turns on "Sneak A/C' when on floor only mode for some odd reason.

Got too lazy to multi quote. Filter didn'[t show a notice with or w/o pre foam filter or STP filter. 

Maf cleaning with spray can help put but also check the map if it's covered in oil.


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## jblackburn (Apr 14, 2012)

Merc6 said:


> Depends on the settings. The compressor is variable so if you aren't on the blue dot to the left of the temp knob it won't go full power.
> 
> Another thing to take note is the Gen 1 turns on "Sneak A/C' when on floor only mode for some odd reason.
> 
> ...


Fan speed and high side pressure controls compressor displacement, not temperature knob.

Max cold on the temp knob closes the recirculate flap automatically.


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