Will not start when below 40 degrees cranks and cranks if above 45 starts but runs ruff till warm

One possible reason for this could be a faulty engine coolant temperature (ECT) sensor. The ECT sensor tells the engine control module (ECM) the temperature of the engine coolant, which is used to adjust the air/fuel mixture for starting. If the ECT sensor is faulty, it may be sending incorrect temperature readings to the ECM, causing the engine to not start in cold weather.

Another possibility could be a weak fuel pump check valve. When the fuel pump check valve fails, it can cause the fuel pressure to drop when the engine is turned off, which can cause hard starting in cold weather .

It's also possible that the battery is weak and not providing enough power to start the engine in cold weather. Cold temperatures can reduce the battery's cranking power, which can make it difficult to start the engine.

I would recommend taking your vehicle to a certified mechanic to diagnose the issue.

Could be as easy as a clogged Air filter/intake or as difficult as a stuck fuel pump in the cold. Could also be dirty/loose battery connections. Have you ever tried a fuel injection cleaner in your gas? I use Lucas Seafoam and it works wonders on my engine ('05 Ford Sport trac), the thing still runs like brand new.

Ignition module may be bad ! Watch this video , this a four cylinder engine , doesn't matter . Test it the same way GM Ignition System diagnosis 1988 Olds Cutlass

Since batteries lose almost half their cranking power at freezing, and since diesels require much higher fuel temps to start than gasoline engines, many recommend using a block heater whenever the temperature is under 35-40 degrees if starting becomes a problem.

tune up,air filter.

Hello.
If the outside temperature is below 32 degrees, your battery loses as much as 15% of the amps that are responsible for turning the engine over.
On your battery you should have a sticker that shows a rating for "Cranking amps," ( CA ) above 32 degrees, and "Cold crancking amps" ( CCA ), below 32 degrees. Your car most likely needs atleast 700 CCA.

Also, if you do not have a maintenance free battery, ( It should say right on the sticker if it is. ), you may want to check the levels in your battery. If the cells are low it will prevent the battery from reaching a full charge.

I hope this helps you

Check the spark coil block and the crank sensor.

You have problem with idle air control valve, it's mounted on throttle body, easy to replace.

I was just reading the owners manual for my 2000 beetle and it says the diesel fuel has a problem with the wax separating from it below 40 degrees. Put the car in a warm garage and it will start.

if you went to Kia dealer last Feb and they did not solve problem and it is still a problem in Dec, then you are the problem. Make the dealer fix the darn thing!