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Discussion Starter #1
Hi,
My apologies if this has already been addressed - I did a search of idle problems and came up with some interesting information but nothing the same as my problem.
First I am a mechanic have been most of my life (I am 60) but mostly Industrial machines and Diesel powered trucks.JD tractors. excavators front end loaders etc.
I have a 2014 cruise with the 1.8 auto 10,000 miles and this problem seems to have started after the first "FREE" oil change. The idle goes to 1400 rpm in stop and go traffic and stays there. Bring the car to a stop and it still at 1400 rpm only way to stop it is to put in N and rev it up past 3,000 rpm then it falls back to 800 or so rpm. The reason I think it started at the oil change is the MPG dropped 2 to 3 mpg since that was done. The reason it took me so long to notice is I don't drive in rush hour 99 percent highway and freeway driving. On tue I was forced to do a parts pickup in rush hour 4 hrs worth to get parts for a Terex front end loader. This is when it became very clear to me as I almost smashed the car in front of me that something was scewed up.

Of course it was in the dealers today and the usual "cannot duplicate customer complaint" I told them it was unsafe to drive and they could have it until they fixed it. So they are going to look at it again monday probably find nothing again and put a black box on it for me to record malfunctions == gee maybe they will pay me to do there jobs too.

thank you for your time

Alan
 

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That's a good one. If it was the throttle body sticking, I think it would set a code. If it was the gas pedal sensor, I'd think it would set a code as well (unless it was the mechanical linkage.) A bad coolant sensor can cause a high idle as the computer thinks the engine is very cold - but the Cruze has multiple temp sensors and will complain if there's too big a disagreement.

'tis a puzzle.
 

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Is this just when you first start your car? My cruze almost always starts on high idle only on hot days its kicks to low idle much sooner. Today for example was 38F when I left in the AM and my car was on high idle for 1-2 minutes of driving and was still on high idle at the stoplight a mile from home.
 

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Yes it is a puzzle it is not setting any codes according to the Dealer. No I have noticed it now with both a half warm engine and I first noticed it when it was completely warm been running for an hour.

The thing that really kills me is I am a mechanic the only one in the shop I work in. I look after 14 tractors, two Volvo semi's 5 semi trailers, two front end loaders and a host of specialty equipment. I am expected to fix and keep every thing running not CANNOT FIND PROBLEM that bs. This is a safety issue and they should be all over it.

Anyway thanks for the replies and I will post whatever they find or should I say whatever I find for them. My money is on whatever they use for the fly by wire throttle.

Alan
 

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My money is on whatever they use for the fly by wire throttle.
But that's the problem. The system has redundancy to find single-point failures. The sensor for the gas pedal is really two sensors - if they disagree, it sets a code. The computer monitors the throttle body to make sure it's moving as commanded. That will also set a code. So you're down to the computer itself - that's an unlikely way for it to fail.

You might want to look at the gas peddle mechanism to make sure something isn't mechanically wrong with it - essentially a stuck throttle. All before it becomes electronic and monitored. I suppose the throttle body could have a issue, and it's just not far enough off to set the code.

The only other thing is something that's causing the computer to want a higher idle setting.
 

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Discussion Starter #6
So took the car back for them to read the "black box" they installed and again nothing. So whatever was stuck is unstuck or the dealer wiggled the right wire or plug in and the problem disappeared. To put it perfectly clear the car did this over a period of 4 hours of rush hour traffic and did it at least 20 times. So something has changed hopefully it wont come back but I know it will and I am going to end up with a smashed front end. Also the things I did while this was happening -- removed the floor mat -- held my foot under the gas petal to force it up, then I stopped and checked for signs of a mouse or critter under the hood no sign -- the car had been sitting for about 10 days while I was moose hunting just prior to this. So again thanks for your input and I guess it is a wait and see.

Alan
 

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So took the car back for them to read the "black box" they installed and again nothing. So whatever was stuck is unstuck or the dealer wiggled the right wire or plug in and the problem disappeared. To put it perfectly clear the car did this over a period of 4 hours of rush hour traffic and did it at least 20 times. So something has changed hopefully it wont come back but I know it will and I am going to end up with a smashed front end. Also the things I did while this was happening -- removed the floor mat -- held my foot under the gas petal to force it up, then I stopped and checked for signs of a mouse or critter under the hood no sign -- the car had been sitting for about 10 days while I was moose hunting just prior to this. So again thanks for your input and I guess it is a wait and see.

Alan
Alan, after it sat for 10 days about how long did the high idle continue. I'm wondering if the battery was in a semi-discharged state and the car was keeping the idle high while it finished recharging the battery.
 

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Is that a thing?


Sent from AutoGuide.com Free App
I have noticed variations in my idle speed from 700 to 1100 RPM and the only thing I can think of that would cause a higher idle is the alternator needing more engine speed to provide more charge to the battery. We have a variable output alternator for fuel efficiency reasons, but variable output implies variable input. Four hours to complete the recharge after being able to start the car seems excessively long to me but...
 

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I was back at work about 4 days before I went on the ill fated rush hour run so the battery should have been good. My run to work is 20 miles each way @ 70mph most of it hwy or freeway only 5 stoplights. Interesting enough the mileage has gone up 3 mpg on the last tank since it left the dealership.
Now I just don't trust the stupid car when I come up to stop lights. I intended to give this car to my son when he turns 16 but if it acts up again and they cant find why then I will just trade it in and let someone else smash up the front end.
Again I thank you for your input.

Alan
 
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