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Discussion Starter · #1 · (Edited)
CMF EDIT: This post has been updated with additional/corrected info by the author. The new corrected form may make some of the following posts confusing.

Please can someone help me with this. If anyone has had this same issue, can you let me know what you did to fix the problem.
So, starting in the middle of Sep my check engine light came on. It was the high o2 sensor. My dad changed this out and a day later the check engine light went off, but then the car started to stall out on a cold start after a minute. I started it back up and it stayed started, but would rumble at low RPM 500. The Malibu 2014 2.5 runs well and seems to be turning over good. In the beg of Oct the car still continued to stall out on a cold start, no codes being thrown since middle of September. My dad cleaned the throttle body and checked out all the vacuums around the Throttle and MAS. No leaks. My dad checked my intake manifold and all the bolts were extremely loose on the intake. He tightened them and I took it in to a privately owned body shop to have the bolts tightened to spec. Still after this, the car continues to stall on a cold start. Last week I took it into the Hugh white Chevy dealership in lancaster Ohio and they told me “We can’t diagnose it if it’s not throwing a code” Jesus man? What has happened to the Trade in this country? Anyhow, I drop some $ down and put a brand spanking new Throttle body in.. the car continues to stall. I ended up having the same dealership put a new MAS sensor in and today 10/30/20 the car is still stalling after the first cold start, but starts back up and drives. No codes being thrown. .! Can someone please explain what the issue may be?
 

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2017 SS Sedan 6.2L
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The only 2014 Malibu with a 2.4L engine is the mild hybrid version, and it's very rare for that year. All others had a 2.5L engine or a 2.0L turbocharged engine. If you search the forum, there have been a number of reports of 2.5L models with rough idling and stalling issues with loose intake manifold bolts, tightening those bolts usually fixes the problem.

Another common issue is carbon build up in the intake ports and valves because of the direct fuel injection system. That has to be manually cleaned out with a process called walnut shell blasting and costs around $300-400. It can be done at home with a lot of elbow grease.

If your car is a 2.4L mild hybrid, it's a totally different animal.
 

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Discussion Starter · #3 ·
isn’t the dealers
The only 2014 Malibu with a 2.4L engine is the mild hybrid version, and it's very rare for that year. All others had a 2.5L engine or a 2.0L turbocharged engine. If you search the forum, there have been a number of reports of 2.5L models with rough idling and stalling issues with loose intake manifold bolts, tightening those bolts usually fixes the problem.

Another common issue is carbon build up in the intake ports and valves because of the direct fuel injection system. That has to be manually cleaned out with a process called walnut shell blasting and costs around $300-400. It can be done at home with a lot of elbow grease.

If your car is a 2.4L mild hybrid, it's a totally different animal.
I appreciate the response! I bought this vehicle from my parents in 2018 with 27,800 on the 2014 Malibu. My father at the time indicated the engine is a 2.4. I am supposed to take the vehicle back to the dealership next week. I’ve mentioned possibly the Fuel pump relay, fuel pump circuit, BCM. I have an Auto technician friend in Texas who has done research on my problem and has Indicated it could possibly be the battery cables that need changed out. If there are anymore suggestions anyone may have, please don’t hesitate✌🏼
 

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That didn't really answer what engine you actually have. It makes a significant difference. Look at these pictures and let us know which looks like your car.

This is the engine bay of a 2.4L Malibu mild hybrid.




This is the engine bay of a 2.5L Malibu.

 
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Discussion Starter · #6 · (Edited)
Sorry, my dad and were wrong. Anyhow, the car has never had any issues ever like this. It’s ran Great since I bought it from them. I also need to mention that I found my gas tank door open in the middle of Aug, and as you prob know these cars don’t come with a locked gas cap. When I noticed this also in August, the gas cap was still on and I did not see any residue of any sort near the cap or ground below. Both places I have taken it have checked the gas and fuel pressure and both said they don’t think the tank was tampered, but I just wanted to throw this out there just to help with a possible diagnosis. This has been very stressful😔
 

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Discussion Starter · #8 · (Edited)
I just drove the car a hour ago. I started it. Cold start. Stalled out sooner than all the other times. I restarted it, it stalled out again. I then restarted it for a third time and it stayed started, a little rumbly, but not as much as it had been on 10/28/20 Wed. As I had mentioned, the dealership placed a new Throttle body in it 10/29/20 the stalling continued and they threw a new MAS in it and the stalling stopped while at the dealership. No codes at all.
 

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2011 Malibu LTZ 3.6L V6 Red Jewel Tintcoat
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Is the air filter clean and unimpeded?

Has the fuel pump relay been swapped with another relay like it, or replaced outright to ensure that it's not dying of fuel starvation?

Are all of the ground cables from the battery tight and clean, as well as the grounding straps to the engine?

I'd get an OBD dongle and use the Torque app to monitor the fuel pressure as well as any other sensors that could tell you something about what's going on. I now use a BlueDriver dongle and their free app and it will read all 4 code families, which is very useful with today's computers on wheels.

BTW, if you ever want to know what size engine is in a car, lift the hood and look at the emissions sticker. It'll have the engine size right there for you.
 

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Discussion Starter · #10 · (Edited)
My air filter was just changed earlier this summer. I’ll make sure it’s in there correctly and is the correct size.
For the fuel pump relay, I was told by a mechanic buddy of mine that it could be something as simple as changing the Battery cables out. I mentioned this to the Dealership. The dealership said the pressure was good on the fuel, and nothing was found in the fuel, but I will mention all the advice you have given. I do take care of my vehicles and I’m very concerned. I don’t want to loose an arm and a leg at the dealership for something that could be as basic as a battery cable change etc.. 🥺

Is the air filter clean and unimpeded?

Has the fuel pump relay been swapped with another relay like it, or replaced outright to ensure that it's not dying of fuel starvation?

Are all of the ground cables from the battery tight and clean, as well as the grounding straps to the engine?

I'd get an OBD dongle and use the Torque app to monitor the fuel pressure as well as any other sensors that could tell you something about what's going on. I now use a BlueDriver dongle and their free app and it will read all 4 code families, which is very useful with today's computers on wheels.

BTW, if you ever want to know what size engine is in a car, lift the hood and look at the emissions sticker. It'll have the engine size right there for you.
Thanks for the advice! I’m going to need it! Single woman, all I have to go by is what my dad has taught me and tons of the correct research and reliable sources.
 

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2011 Malibu LTZ 3.6L V6 Red Jewel Tintcoat
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Before you wander off to pay someone to do more, pull the fuel pump relay, look at how many pins it has, then find another one with the same and swap them.

If the problem persists, then the relay is not likely the cause.

Any work done at the dealership will cost, and it's quite often more than independent shops. I'm not saying not to go there; just making you aware that you have options. Either way, it'll cost you money.

What I don't see is any mention of the intake valves being inspected for crud, as mentioned in post #2 by @cp-the-nerd. If the car runs fine otherwise, spend some time and try to look at them yourself. If that's not possible, then consider adding those to your laundry list.

The new TB was probably just a guess by the shop, and now that it hasn't panned out as the cause, it can be considered a costly lesson in what not to do. Don't just go throwing parts at the car. Find the cause, use logic, and make the shop prove that the part they say you need is actually needed, or else they can put the original part back on and charge you nothing for their sell-you-parts-just-to-make-you-feel-better tactics.
 

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My guess is loose intake manifold bolts. Vacuum leak on a cold start will lean stall the engine. After warm up and expansion it seals more. I had a Sable with leaky intake gaskets and it would cold stall and be fine after warm up.
Vacuum leak is probably more than system can compensate for when cold. Checking those bolts would be a good step since it's been reported by others.
 
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Discussion Starter · #13 · (Edited)
I don’t work on the cars, my father usually does and he is old and grouchy and doesn’t want to mess with it. His exact words “Chevrolet built the SOB, let them figure it out”. I’ve already spent some money for the throttle body and MAS. I'm very hesitant on going back because obviously they don’t know what it is, but I don’t know what else to do.
 

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2016 Malibu 1LT 1.5T/6-speed 6T40
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I believe the intake manifold bolts were already checked, tightened, and double checked. That is a good item to cross off the list because it is very common. Following that I would want to see about actually replacing the manifold gasket since it was loose for so long.
My dad checked my intake manifold and all the bolts were extremely loose on the intake. He tightened them and I took it in to a privately owned body shop to have the bolts tightened to spec. Still after this, the car continues to stall on a cold start.
 
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Discussion Starter · #15 ·
The manifold bolts where loose as a goose, you could hear the bolts rattling when my dad was tightening them. I just had the alternator and battery checked and air filter. All good. Car idling good at 500RPM no rumble or stalling. It did stall about 45 minutes ago when I first started it up since 430a this morning.

Drivendaily, thank you for all the input. I’m going to pass what you said along and try to start dealing in parts and find someone trustworthy to look into it and help me. The dealership said they would keep trying to figure out what is wrong with the car at no charge, but if they need new parts.. I’m pretty much screwed. I may just have to breakdown and see if my dad will help. This really sucks with Winter coming. 👎🏼

Thanks for the words of wisdom! This is the first time I’ve had to do this by myself.
 

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Not sure if this will help, but you said this started after changing the o2 sensor. Did you use an aftermarket brand or did you use oem (ac delco)? Sometimes chevys are very picky with their sensors and computers working together, and if it starts fine then stalls out after a minute, it sounds to me like there is a possibility of the sensor not reading exactly how the engine wants when going into closed loop (running off the o2 sensors to get the right air fuel mixture), causing it to stall out do to improper air fuel mixture. Just my two cents, hope you figure out your issue :)
 

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Discussion Starter · #17 ·
It’s worth looking Into. At this point in time, I’m writing all this down and when I can find someone to help me tear into it, I’m going to check everything that everyone on here has suggested. Thanks Smtcoil✌🏼
 

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Possibly the intake manifold gaskets got damaged from bolts being super loose. Like I said in post 12 my Sable would only act up with a cold motor. And it was a V6 that did not have the free hanging 4 cyl. manifold.
 

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Discussion Starter · #19 ·
👍🏼. I’m just documenting what it does everyday and continually searching for possible fixes. God help me!😂
 

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Since it appears your dealer wasn't able to find the issue since there is no fault code, you might consider taking it to an independent shop so they take the time to connect a scanner and monitor on cold start. Something with fuel might show there. It is true, if the problem is electrical or engine related dealers tend to look for a fault code. Reading they just tossed parts at it is disappointing. Unless of course they found codes and replaced based on those codes and just didn't tell you. Sometimes issues have more than one cause... but it sounds like a part toss to me. Beyond that, if you are looking to toss your own parts, a couple of us recommend the intake manifold gasket since the bolts were wiggle loose. Speaking of which - have you tried disconnecting the battery for 20 minutes following tightening of those bolts? It might need to relearn if there was that large of a leak.
 
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