The coolant temperature sensor (CTS) could be the problem with cold start problems. It was on my 2005 Aveo LT. Had terrible time starting when cold. Actually hard to start after sitting 8 hours or more in 70+ degree weather. I tried several things before I found the actual problem. A defective sensor does not set a code. So for me it was try this and then something else.

As it turns out the CTS was the least expensive part to buy but the hardest part to get access to on my Aveo. Forget about testing it. If you get to it, replace it. I could only access it from below the car when it was jacked up. The CTS screws into the back side of the engine block below the intake manifold, between the engine and the firewall. There is an engine brace which is in the way and must be removed. It has 4 bolts in it. The bottom two bolts are #14 metric the top two are #13 metric. The top ones required me to use a short extension to remove. Once the bracket is moved to the left side of the car you can access the CTS. There is a clip on the two wire connector which must be released. This is tricky using only one hand. Once the wire is removed you can access the CTS.

Remove the pressure cap on the water inlet tank. When you remove the CTS water/anti freeze will come out of the hole. You may want to drain the coolant first. I did not. You will need a 3/4 inch SAE deep-well socket to remove/reinstall the CTS. It comes out easily once loosened. Good Luck, sorry no pictures were taken.