Hyundai Repair: Hyundai Sonata 2.5 V6 1999 manual wont start, coolant temperature sensor, air flow sensor

Question
Hi, My Sonata has developed a problem that the dealer can't fix although he has replaced the crankshaft sensor and spent many hours trying. The car always starts fine when cold and generally performs quite Ok however frequently after driving a couple of kilometres and leaving the car for around 10 minutes the engine will wind over fine on the starter but will not fire at all. Leave the car for a few more minutes and it will eventually start roughly and appears to have a very rich mixture and will blow smoke out the exhaust. You can drive off though the engine is low on power and running roughly and the accelerator does not respond smoothly through its stroke - like a dead spot then the engine will respond like full throttle then die (but not stop)when you back off the throttle. It is quite vicious with the power on then power off as you move the throttle.
Hope this makes sense.
Ken  

Answer
I'd suspect a faulty coolant temperature sensor.  It can make the mixture so rich that the car won't start as well as explain the smoke from the exhaust.

But this is still mostly a guess.  Could be a problem with the air flow sensor or the air intake bellows as well.  Unfortunately, it'll probably take someone diagnosing the car while the condition is occurring in order to solve.