Starts fine, after 30 min idle is skippy

[FitusMilbarge]

I have a 2012 Sonic Sedan Standard. When I start my car the idle is fine, acceleration is fine, and I have no problems. After i drive for about 30 min through the city when i come to lights and have to stop i notice my idle is fine for a few second and looks as if it idles at 800-900 rpms. Occasionally it dips to 600-700 and it feel like the car skips a beat before it catches itself and gets back to 800-900. The skipping is inconsistent. I noticed i was a tad low on oil and added some the other day to see if that was the issue and it was not. I also replaced my spark plugs last month, today i rechecked the gaps and reinstalled. I had no issues since the new plugs were installed for the last month until 2 days ago so i dont think they are the issue. Car is stilling at 93,000 miles.

Could this be a belt issue? Should i try cleaning all the intake pieces? Sine it drives fine and there is no acceleration loss while driving i dont think its a fuel or air delivery problem but i could be wrong.

 

[sonic daddy]

Cant hurt to clean the intake out with sort of cleaner such as sea foam or something similar don't think your timing belt will cause this issue

 

[gnonne]

Check for a cracked air intake tube between the filter box and the intake manifold. They all do this. It might be just starting on yours and not throwing a code yet.

 

[JTee2017]

First. . get a decent OBDII scanner for $80 to $100 and check for spark plug misfires, O2 sensor readings and pending codes, when the engine is hot and problem is occurring. Since the idle is varying, that could be it or any of the other things members have pointed out above. People forget that before a "check engine light" is triggered there can be pending fail codes that often will shed light on intermittent engine troubles.
You can also take the car to a Autozone, Advanced Auto, O'Reilly's, etc store and usually they will connect a scanner (hopefully a good one) that can show pending codes.

Since you recently changed the plugs which requires removing the coil pack . . maybe check the connector to it as well as the individual coils themselves.

Since it starts a runs fine but acts up after 30 minutes or so and heated, maybe a coil is going out, cracked, etc. They don't last forever and when removing the coil pack, they can get stressed and even get a hairline crack.

If the coil pack was never replaced, I would just do that as a matter of routine with on a 6 year old sonic.

Plenty on Ebay from original OEM GM to after market ones. . . maybe $50 to $80.

https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=Chevrolet+SOnic+coil+pack&_sacat=0

 

[sonic daddy]

My sons 2012 sonic developed a rough idle took it to a shop he lives in Florida they said his coil pack was bad they wanted $445.00 dollars to fix which he didn't have he ordered part off line coil pack and 4 new spark plugs a friend of his helped him fix it car runs great now.

 

[FitusMilbarge]

I will have to try the coil pack. I cleaned the intake parts and belt is fine. Driving home just now the check engine lights started blinking, the TCS light came on for some odd reason and the engine has a mean vibration now. No long a smooth idle but its rough.

 

[JTee2017]

I will have to try the coil pack. I cleaned the intake parts and belt is fine. Driving home just now the check engine lights started blinking, the TCS light came on for some odd reason and the engine has a mean vibration now. No long a smooth idle but its rough.

The only other thing you could check is the battery condition, check ground connections, and clean the battery terminals. With the lights coming on like you say, something electrical could be going on. On these cars with Engine Control Modules, sometimes a battery will start to have a bad cell and voltage will drop to 10 volts or so. That is enough to cause faulty operation.

Even if the battery is newer, if it has been on a shelf long before being sold, it can suffer an early failure.

 

[FitusMilbarge]

Replaced the Coil pack and only let the car run for 5 min or so but the awful vibrations are gone!

I tested the battery as you suggested and still getting a 13+ so i think im good to go there. Tomorrow when i take it for a spin will be the real test!

 

[FitusMilbarge]

Happy to report that my drive to work this morning was back to normal. No rough idle and acceleration was back to the best its ever been.

Thanks to all for the suggestions, and JTee2017 that coil pack did the trick! Since i just crept over 94,000 miles i have ordered a new belt, water pump, and pully kit. Not looking forward to installing those in 20 degree weather but it needs to be done.

 

[JTee2017]

Happy to report that my drive to work this morning was back to normal. No rough idle and acceleration was back to the best its ever been.

Thanks to all for the suggestions, and JTee2017 that coil pack did the trick! Since i just crept over 94,000 miles i have ordered a new belt, water pump, and pully kit. Not looking forward to installing those in 20 degree weather but it needs to be done.

Hope that did fix the misfires. The thing is, these engines can be kept running with some routine repair items for pretty low cost and most are user doable.
On the timing belt, pulley, tensioner and water pump. . . make sure you have the kit to lock the cams in the exact place ( it isn't as many expect) and look up that procedure. It is a bit fussy to do. There are a couple Youtube videos on the Chevy Cruze 1.8L as well showing how to do it.
Myself. . I might look for a good repair shop to do it after you buy the parts. Especially in cold weather. Not something you want to go awry and damage the engine if cam timing gets screwed up and a valve hits a piston top. In the cold, hands get numb, wrenches slip, mistakes get made. And there is little room in there to do the work. A heated garage is best.
Otherwise, if you aren't going to put a lot of miles on it. . . it would probably make it to spring. You could always just remove the timing belt upper cover and see how it and the pulley looks for wear and cracks or shredding. . . .

 

[FitusMilbarge]

I did some poking around the engine yesterday when i installed the cold air intake and the temp was in the 50's so it was the best day to be outside in the last 2 weeks. The belt looks solid now that i had a chance to take a peek at it. Seems like the dealership i bought it from when it had 85,000 miles on it had already replaced the belt before they sold it. Might just hold onto the kit until something noticeable happens and warrants the belt, water pump,or pulleys to be replaced

 

[JTee2017]

I did some poking around the engine yesterday when i installed the cold air intake and the temp was in the 50's so it was the best day to be outside in the last 2 weeks. The belt looks solid now that i had a chance to take a peek at it. Seems like the dealership i bought it from when it had 85,000 miles on it had already replaced the belt before they sold it. Might just hold onto the kit until something noticeable happens and warrants the belt, water pump,or pulleys to be replaced

Um mm . I wouldn't assume the dealer replaced the timing belt. First . . it is a $600 to $800 job with labor. Second. . . you would need to inspect the pulleys for wear. If they look dirty (belt dust, etc) on the outer part and worn on the part contacting the belt , I doubt they were replaced.

Lastly. .. "to wait til something noticeable happens" could be very risky since the the thing that happens would likely be dropped valves into the pistons and a totaled engine. If you have no proof or replacement but things look OK under there for now, it might be wise to just replace all of it when warmer weather arrives.