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Discussion Starter · #1 ·
I've noticed lately with the colder months, and running rear defrost and heated seats and heater for blower that when I seem to pull or draw a lot of electrical demand at one point, the RPMs actually drop from my idle of almost 600-800 RPMs to almost as low as 400 and its real rough and louder than my normal idle. I'm not anything of an auto mechanic handyman, but with seats, rear and front defrosts on, when I go to use window up and down that they move slow and the idle becomes real rough


2011 Chevy Cruze LTZ 1.4L Turbo
 

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Your alternator will put more of a load on the engine depending on your electrical load. Fun fact some BMW's even try to limit the alternator's charging at lower speeds in order to help fuel economy.

Does this occur only when you are warming up at the start of your drive or just anytime you are driving with all of those components running?
 

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No surprise that the the heavy electrical load translates to a engine load. Just kind of odd that it's not compensated for and more throttle isn't commanded to bring it back up.
 

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It likely has little to do with the electric load and more to do with the defrost for the front and read both requiring the ac to be active to dehydrate the air. Notice that there are little vents on the rear deck that will actually blow a bit when defrost is on back there.

Your electric load is probably high, especially at those times because the systems and Ac do require a lot of power as the heater in the seats and the rear defrost is basically a resistor path.

The electric load isn't helping either. These engines produce little torque at idle so they have more trouble overcoming the extra loads on it.
 

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454 CID doesn't have this problem an 86 CID engine sure does, alternator rated output is 120 amperes, but only capable of producing this kind of output with an engine speed of 2,500 rpm. When these small displacement engines were introduced, some form of idle speed control had to be added.

Typical was an IAC idle air control valve, simply a valve that would let more air bypass the throttle body, but the Cruze uses throttle by wire, so the IAC is not needed, throttle valve is opened by the BCM for idle boost.

Wondered about this in particular with the PCV returning back to the input of the turbo, as the engine wears most blowby in the piston rings, more crap returning back through the throttle body vane with soot that can hamper its movement. So it can be receiving commands to open, but stuck. Fords really had this problem returning the PCV to the air cleaner that would retard the vane in the throttle body. Honda's were far more intelligent to return the PCV to the base of the throttle body.

In this respect, consider TBW another PITA, can put your fingers on the linkage to feel if the vane is sticking, and this is not the easiest TB to remove for cleaning, but can peek in there to see if you have soot in there. Carbon is the problem, been this way for over a hundred years, builds up on the piston rings and even locks them so they can't expand anymore.

One reason why I am treating my vehicles frequently with Seafoam, not going to get into what kind of carbon cleaner is the best. But the way the Cruze is set up, can also cause the TV to get sticky that may well be the cause of your problems. How many miles on this thing?

There is a learn procedure for idle boost in the Cruze, goes like this.

"Throttle/Idle Learn

The Idle Learn Procedure listed below must be performed whenever the following occurs:

The crankshaft position variation learn procedure is also required when the following service procedures have been performed, regardless of whether or not DTC P0315 is set:



  • The throttle body assembly is replaced
  • The throttle body is cleaned
  • The engine control module (ECM) is replaced
  • The idle air control valve is replaced
  • Power disconnection (battery cable, ECM fuse, etc.) (Delphi ECM only)

  1. Turn the ignition ON.
  2. Turn the ignition OFF for 15 s.
  3. Turn the ignition ON for 5 s.
  4. Turn the ignition OFF for 15 s.
  5. Start the engine in park/neutral.
  6. Allow the engine to run until the engine coolant temperature is greater than 85°C (185°F).
  7. Turn the A/C ON for 10 s, if equipped.
  8. If the vehicle is equipped with an automatic transaxle, apply the parking brake. While pressing the brake pedal, place the transaxle in drive for 10 s.
  9. Turn the A/C OFF for 10 s, if equipped.
  10. If the vehicle is equipped with an automatic transaxle, while pressing the brake pedal, place the transaxle in park/neutral.
  11. Turn the ignition OFF. The idle learn procedure is complete."


For extra protection on the alternator output, a current sensor is located in the negative battery cable that will limit the maximum duty cycle of the field current. For the most part, I find rear window defrost to be next to worthless, so use a scrapper, this adds another 25 amps to the alternator load, electrically heated seats are also hungry, blower with AC pulls another 20 amps. Alternator can handle this at 2,500 rpm, but certainly not at 600, radiator fan is also hungry.

But your idle speed should hold even though with all this stuff on, will be drawing the excess current from the battery, and this is the worse time as your battery just had a starter load on it. Could sit in your car in neutral and hold the tach at 2,500 rpm until it warms up, or just switch stuff off. With an AT, have to be a low idle or will really stress your torque converter. That fluid is ice cold.
 

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Discussion Starter · #6 ·
Does this occur only when you are warming up at the start of your drive or just anytime you are driving with all of those components running?
Anytime I idle, I notice a rough idle but no significant drop in Rpms when I have a large load on the electrical. So I can start the car, drive a little bit then park and idle and same thing.


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Discussion Starter · #7 ·
Also, every cold New England morning I warm the car up or at least 5-10 mins before shifting it. This happens whether I'm idling off a start or idling after driving a bit but doesn't seem to bottom any Rpms when I'm driving or at a red light I should say, just a rough idle then but without any electrical load my car is smooth.


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With a pre-EPA 455, could remove even three spark plug wires and still drive at 70 mph on the interstate, EPA said we got to do something about this. With even the slightest misfire that little 86 CID engine practically dies, screws up the computer.

Even when I notice the slightest hesitation, pulling and cleaning my spark plugs, get even the slightest carbon on that center electrode spark plug insulation, that is shorting that voltage to ground. On the Cruze, also have to make darn sure those springs for conductivity are not hung up in the boot shoulder.

Even the slightest misfire can start cooking your cat, an aftermarket exhaust system won't cure this.

You guys could well have too large of a gap on your plugs, hung up springs, and a bit of carbon on them causing your hesitation and low idle problems. 25 mil gap even works much better than a 28 mil cap, those coils are sub miniature.
 

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.....Even the slightest misfire can start cooking your cat, an aftermarket exhaust system won't cure this.

You guys could well have too large of a gap on your plugs....

:O

Oh no, now I'm worried my car has too many parts and they're all gonna go wrong.
Cars are way too complicated.
 

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:O

Oh no, now I'm worried my car has too many parts and they're all gonna go wrong.
Cars are way too complicated.
Spark plugs are too complicated? But can agree with BCM's and made in China point contact relays replacing real sliding contact power switches. And really liked the manual windows and cabled controlled MVAC system in my 04 Cavalier.
 

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Spark plugs are too complicated? But can agree with BCM's and made in China point contact relays replacing real sliding contact power switches. And really liked the manual windows and cabled controlled MVAC system in my 04 Cavalier.
Cars in general are too complicated, it seems like I'm always worried about something that might go wrong, or some noise I think I might be hearing. I understand how spark plugs work and how to check and change them. I just hate having that constant worry when I read someone else having an issue that I might be having that issue too. Now I'm gonna have to check my spark plug gap.
 
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