Weird things going on with Sonic

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Fluffycakes2020

Member
Ok so i own a 2012 Sonic with 1.8 and recently i have been having weird idle problems. So I looked into it, checked and cleaned throttle bottle, was going to check spark plug gap when i saw that two plugs had a bunch of oil in them. Took the plugs out and regapped them and changed the valve cover gasket. Problem solved, for now. Problem comes back. Basically what its doing is while im at a light, it will vibrate every 4 seconds or so and the rpms will drop when it does and the lights will dim as well. Also, maybe unrelated but while driving on the freeway the other day, the headlights dimmed and the battery light came on and turned off and did it a few times while driving 65mph+. Last night, while at a light when it was idling bad, it just turned off. Luckily it turned right back on. I have seafoam I plan on trying to run through vacuum system to check for leaks, and possibly put in gas tank. Havent checked the spark plugs to see if oil is back in there but will soon since that fixed it.

Any other ideas that I can check for?
 
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Gobinator98

Member
Why are you even thinking about using seafoam to check for leaks? That’s not even a recommended way. You say that it happens only at lights or while you are driving highway speeds, if so, it’s not going to be a vacuum leak because a vacuum leak does not really affect an engine at all while cruising at higher rpm/speeds.

One thing you should definitely check is the serpentine belt since you said your battery light goes on and off. Your tensioner could be failing and causing the belt to be loose and slip.

Two, is your oil leaking again? If it is, it might be your head gasket. I had to replace my engine @ 125K because of a head gasket failure while on the interstate.

Three, I don’t really have anything other advice besides getting your car scanned for codes. There is most likely pending codes stored and they only stay for so many drive cycles before they are gone or are confirmed.


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Fluffycakes2020

Member
I was only thinking of using it to see if theres build up somewhere and to try and clear it out.

It only did it a few times yesterday. I drove today and the light never came on but it still idles bad.

I havent checked but if i have time today i will check to see if theres oil on the spark plugs.

I will also check with my obd2 device and see if there are any saved codes that can point me in any direction.
 
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Fluffycakes2020

Member
Ok so I checked the spark plugs and no oil so valve cover gasket it is. Now trying to find the source of the bad idle. The battery light only came on today one time but that was it after the original time so not sure. What can I use to see if there's any possible vacuum leaks to rule that out?
 
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Gobinator98

Member
Fluffycakes2020 said:
Ok so I checked the spark plugs and no oil so valve cover gasket it is. Now trying to find the source of the bad idle. The battery light only came on today one time but that was it after the original time so not sure. What can I use to see if there's any possible vacuum leaks to rule that out?
Click to expand...


If you got someone that smokes cigars, you could have them blow smoke into a vacuum line then plug the opening you created to force the smoke to find another way out. Or you could go on amazon and buy a dedicated leak detector that you hook up to an air compressor. I thought you already replaced the valve cover gasket? Or was that the valve cover itself? If it was the valve cover that you replaced, you should’ve replace the gasket too.

You also said that there was no oil by the spark plugs, that means your gasket is fine.


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Fluffycakes2020

Member
I did change the valve cover gasket which is what i was hoping would fix oil on the spark plugs which it did. I checked that today and all was good. I checked the purge valve and its good. I suppose thats a vacuum line in that so I could probably put smoke in there to see if theres a leak. If it passes than I kinda dont know where to go from there.
 
JTee2017

JTee2017

Well-known member
Does the Check Engine Light come on at all?

If so, of even not, check the vacuum lines.
One thing that sometimes happens is the vacuum line connector from the intake manifold to the power brake booster cracks or gets loose. Wiggle it or press into the connector at the right side of the intake manifold.
This can not easily be seen so use a good LED flash light to see what you're doing.

You could also have the usual cracked air intake tube from the air cleaner to the throttle body.
 
SuperFudd

SuperFudd

Member
Electrical?

I would bet an intermitant electrical problem. I would monitor the voltage at the cigarette lighter, since I have a meter that plugs in there. If the voltage drops occasionally I would then measure voltage at the battery and go from there.
 
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Fluffycakes2020

Member
JTee2017 said:
Does the Check Engine Light come on at all?

If so, of even not, check the vacuum lines.
One thing that sometimes happens is the vacuum line connector from the intake manifold to the power brake booster cracks or gets loose. Wiggle it or press into the connector at the right side of the intake manifold.
This can not easily be seen so use a good LED flash light to see what you're doing.

You could also have the usual cracked air intake tube from the air cleaner to the throttle body.
Click to expand...

No check engine at all. Checked the intake tube when I took it off, no cracks. I wanted to check vacuum lines but with spray to quickly identify it. I haven't checked any connectors but can do that as well.
 
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Fluffycakes2020

Member
SuperFudd said:
I would bet an intermitant electrical problem. I would monitor the voltage at the cigarette lighter, since I have a meter that plugs in there. If the voltage drops occasionally I would then measure voltage at the battery and go from there.
Click to expand...

Could be electrical but I haven't checked into it. Guess I'll have to get one of those voltage cigarette lighter readers.
 
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Gobinator98

Member
Fluffycakes2020 said:
If anybody sees this do you think my problem could be O2 sensor related?
Click to expand...


Your best bet would be to have somebody with a scan tool to look at any pending or confirmed codes the car has(light doesn’t have to be on) and have them look at the live data while the engine is running. More specifically, the short/long term fuel trims, fuel pressure, air intake volume( in lb/min), and the readings from all oxygen sensors.
If you don’t have a scan tool available to use that can read live data, BlueDriver is $99 dollars and can do all of that and more. You just buy the Bluetooth dongle and download their app and you are all set. If you need anything else, like how to read the live data, just send me a pm and I’ll try to help you out. I had an idle problem not that long ago and looking at the live data helped me solve the problem. Also, if you do get the BlueDriver, you can export the live data into an excel file or pdf I believe and then I could look at that more closely to help determine what is wrong.


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Fluffycakes2020

Member
Im Glad you mentioned that because I actually have one those readers and have been looking at the live data which is why I suggested the oxygen sensor. I have screen recordings in my phone and once I figure out how to upload them here I'll show you.
 
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Gobinator98

Member
I took a look at them videos.

Fuel trims: Short term looked normal to me. Should not be lower or higher than -10%/+10%.
Long term fuel trims shouldn’t be much higher/lower than the short term. Based on the amount of video you gave me, I can say you have some sort of small vacuum leak but nothing like I had. Could you possibly get a video of the fuel trims that is like 15 minutes or longer? Just so I have a better idea of what is going on with the fuel.

Oxygen sensors: the voltages looked just fine from what was shown, so your sensors are working the way they should.

Other data: The only thing that looked useful from the last video was the engine’s rotation. ~670rpm is normal for the 1.8L engine once it is fully warmed up.


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Fluffycakes2020

Member
Ok I will try and get that today if possible. I'm gonna upload 2 videos I took, one video shows what the car is doing and the other is gonna be the engine running from inside the engine bay.
 
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Gobinator98

Member
After watching that longer video, I’d try looking around for a vacuum leak, like a ripped intake boot, vacuum line that came loose or something. Mine had long term trims that got all the way to the computers max value of 37ish percent. Yours only got to about 10ish percent, so you got a small leak. Did you try reseating the valve cover to make sure it sealed correctly? The pcv valve bad? Bad intake gaskets? I don’t know what else to suggest at this point since you have already check quite a bit of things


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Fluffycakes2020

Member
So the intake boot isn't ripped since I checked it cleaning the maf, I assume reseating the valve cover is just taking it off and putting it back On right? The pcv valve is on the valve cover and I couldn't take it off without breaking it so if I reseat the cover maybe I'll just buy the pcv valve and replace it anyways. I just really don't know what to look at anymore
 
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