If your vehicle is showing hard to start when engine is cold, here are the most likely causes and the parts you'll need to fix each one.
Cold weather significantly reduces a battery's cranking power while simultaneously making the engine harder to turn over. If the battery is old or degraded, it won't spin the starter fast enough to start a cold engine.
The engine computer relies on this sensor to know the engine is cold so it can provide a richer fuel mixture. If the sensor falsely reports a warm engine, the mixture will be too lean to start easily in the cold.
A failing check valve in the fuel pump or a leaky fuel injector allows fuel pressure to drain back into the tank overnight. The engine has to crank for an extended period to rebuild pressure before it can start.
Cold, dense air and a rich fuel mixture make it harder for a spark to jump the gap. Worn spark plugs or weak ignition coils will struggle to ignite the fuel when the engine is cold.
The IAC valve must open wider during a cold start to provide extra air for a fast idle. Carbon buildup can cause it to stick closed, starving the engine of air and making it hard to start or keep running.
Intake gaskets can harden and shrink in cold temperatures, creating a vacuum leak that causes a lean misfire. As the engine warms up, the gasket expands and temporarily seals the leak.
Using an oil that is too thick for cold weather (often done mistakenly during a recent oil change) creates excessive internal drag, making it very hard for the starter to turn the engine over.
Worn piston rings or poorly seating valves result in low compression, which fails to generate enough heat to vaporize cold fuel. This is a major mechanical failure that is most noticeable during cold starts.