1999 Malibu hard start in hot weather, after it starts runs great lots of power. starts when cold in cooler weather.V6 3.1 engine. have gas at rail. changed spark plugs and wires, IAT and ECT sensors also replaced IAC. Help

How to Start a Car in Freezing Cold Winter Weather

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wikiHowFreezing cold weather can take a toll on car batteries. ... It's much more difficult to start a cold car with a mostly-empty tank, so do yourself a favor and gas up ...

Why is it so hard to start a car in the winter? - HowStuffWorks

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To start a car in winter, your engine has to work extra hard. Learn the top 3 reasons your car is hard to start in cold winter weather.

Debunking 5 Cold-Weather Car Myths - Popular Mechanics

Reason 1 - Gasoline, like any other liquid, evaporates less when it is cold.You have seen this -- if you pour water onto a hot sidewalk it will evaporate a lot faster than it will from a cooler place like a shady sidewalk. When it gets really cold, gasoline evaporates slowly so it is harder to burn it (the gasoline must be vaporized to burn). Sometimes you will see people spray ether into their engines in cold weather to help them start -- ether evaporates better than gasoline in cold weather.

Reason 2 - Oil gets a lot thicker in cold weather. You probably know that cold pancake syrup or honey from the refrigator is a lot thicker than hot syrup or honey. Oil does the same thing. So when you try to start a cold engine, the engine has to push around the cold, gooey oil and that makes it harder for the engine to spin. In really cold places people must use synthetic motor oils because these oils stay liquid in cold temperatures.

Re ason 3 - Batteries have problems in cold weather, too. A battery is a can full of chemicals that produce electrons The chemical reactions inside of batteries take place more slowly when the battery is cold, so the battery produces fewer electrons. The starter motor therefore has less energy to work with when it tries to start the engine, and this causes the engine to crank slowly.

All three of these problems can make it impossible to start an engine in really cold weather. People either keep their cars in heated garages or use "block heaters" to get around these problems. A block heater is a little electric heater that you plug into the wall to keep the engine warm.
i hope it was convince answers

Gas would leak out of a cold, hard, rubber fuel line. When the car warms up, the rubber line swells and seals itself up until it gets cold and leaks`again. Find that leaky fuel line asap or you're risking an engine compartment fire every time your car is started, when it's cold out.

Is it gas smoke or simply condensation in the exhaust system...in cold weather the catalytic converters run very hot and when the engine cools it cause moisture to build up and when the engine is started it is not uncommon for moisture to exit the tail pipe with a little vapor.

A common problem with the 90's engines was the ECTS (electronic coolant temperature sensor) going bad. Seems when attempting to start the car, the computer in the car will only allow enough gas it thinks is needed to start. When a car is cold, the computer gives more gas initially, until the engine warms up, then gives less gas. When starting a warm engine, less gas is needed.

If the sensor goes bad, it always tells the computer that the engine is hot. The computer give less gas to a cold engine, and sometimes it will start, sometimes not. Its a pretty cheap part, and a do it yourself one, just research it a bit on line...good luck

Sounds like the coil has gone bad. This is usually the syptoms of this. When it is in the non crand status cool the coil down quickly with ice and see if it doesnt crank.

you may be experiencing vapor lock you will have to open you gas cap from time to time in extreme hot weather to let some air into your tank.or have a gas line cooler installed on yur vehicle.

It sounds like your carburetor is flooding, check to see if the choke is set too tight.
to do this, when the engine is cold, remove the air cleaner assembly, push the gas pedal one time to the floor. in the carburetor throat is a flap, this flap closes as engine cools so the engine receives more fuel for cold weather starts, the flap is at the top of the carb. this flap should have about a 1/8" gap between the throat wall and the flap when it is fully closed, if if is completly closed it will give the engine to much fuel and cause it to flood. if you need to adjust just follow the linkage that the flap is attached to, and it will lead you to the choke housing, this is where you can adjust it.
once this is done start the engine and let it warm up, as it warms up this choke flap should open completly up in a vertical position.
if it doesnt, then you probably have lost power to the choke housing or your heat tube that comes from the exhaust manifold to the choke housing is bent, off or missing. most likely yours will be electric.
i hope this helps, good luck

try cycling the key on and off 5-6 times before cranking. let me know what happens

The most common cause of this condition is the check valve in the fuel pump failing, to check this hook up a fuel test guage to the fuel rail test port, run the engine for a moment and shut it down, after shout down the pressure should stay within 5 PSI of the pressure at shut down after sitting overnight, if it doesn't then the fuel pump must be replaced, the reason is the fuel drains back to the tank if the valve is defective, so you get air and no real pressure on cold start, A check of pressure on a hot running engine will not show this fault, also make sure you are usine the correct Octane of fuel, Prem fuel in a regular fuel engine will cause cold start and stalling issues in cold weather.