Hello; I have a 2012 chevy sonic 1.8 I have been having the same reoccurring problem. Just recently every time the vehicle sits for longer that 10 hours I try to start it it dies immediately after it starts. Sometimes it will do it once and start right back up like normal but sometimes it will happen multiple times, and when it is doing it several times in a row sometimes it runs but it shakes and sputters, then if i give it gas then dies out again immediately. Then on the fourth or fifth time i try to start it, it will start right up and idle normally. It only does it when the car has not been started for a day and engine is cold. After about five times it will sputter and shake and then smooth out and is good for the rest of the day. There is no codes on the reader or car.Tried the new gas and Seafoam additive. A little better but still have to try 3 to 4 times before it starts. Starts then slowly dies in about 3 to 4 seconds. Have to do this about 4 times until it runs normally, then everything is fine. the plugs have not been changed. the car has 110,000KLM on it. The reason I was trying the gas is that there was no problem with starting the car until I filled it up a day ago at a CO-OP Gas Bar. then when I went to start it this problem started. The car keeps turn over and barley starting then it shakes and stalls. does this about three to four times. then I turn the key and it starts, and it runs perfect all day even when turning it off and restarting it. It only happens when the car has cooled down and sat for around twelve hours. The engine is stock. Local garage did fuel pressure check and checked for codes and starting system. Everything checked out ok. He said that he seen a service bulletin about a carbon build up on the valves from chevy. He said he pulled a plug and looked into the cylinder with a scope and seen some carbon build up on the intake valves. He used a cleaner that he spayed into the intake and told me to drive it for a week and it should clear it up. I know that usually a carbon build up on the valves or piston top would cause detonation, but can't see if it is that why it would not run rough even after warming up as you would never have a completely sealed combustion camber. So that is my story to this point. Gary

 

they did a fuel pressure check but what about fuel pressure leakdown? Problem could be fuel leaking into the cylinders from the injectors or back to the tank from the fuel rail due to a bad check valve in the fuel tank.

 

Changed the radiator ETC Sensor and now everything is ok. Was giving a reading of 62F when it was 36f temp outside. Thanks for your suggestion thou. Gary

 

that would have set a rationality code and turned the check engine light on.

 

For some reason it didn't give show code. When the reader was put on, that's when the sensor showed the problem.

 

the vehicle does rationality checks on start up, after the vehicle has sat off for a period. It compares the ect, iat, ambient air temps and they should all be near the same reading...if one is skewed, it knows something is wrong.

 

I also have that problem, the car does not start and the ECT sensor of the radiator and the engine has good resistance, the spark plugs have a spark, the injectors have a pulse, it has gasoline pressure, it has cylinder compression, it only marks the temperature code of the thermostat !!!!!! In the morning I have to put some gasoline in the intake and it starts until it stabilizes