When starting the car, I turn the key but the car does not start immediately. I must stop and turn the key the second time, and it always starts. Sometimes... rarely it starts on the first try.

A year, make, model, and engine size would help but I will through this at you.

Instead of just trying to start the car turn the key to the run position and wait 3 seconds. Turn the key off and immediately turn the key back to the run position and wait another 3 seconds. Turn the key off then try to start. Do this every time you try to start the car. If you symptom never occurs when you start the vehicle like this than I would suggest taking a closer look at the fuel system.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

I bet it has a hard time starting after you drive it for a while, make a 10 minute stop, and then try to start it?

If this is the case try this the next time you think it will not start. Turn the key to run but do not attempt to start the vehicle. Wait 3-5 seconds. Turn the key off. Repeat this 3 -4 times. after the fourth time attempt to start.

If it starts every time than you either have a bad fuel pressure regulator or a bad check valve in the fuel pump. The regulator is located on the fuel rail near the throttle body. there is a small vacuum line running to it. remove the vacuum line and see if gas come out of the regulator. if it does replace it immediately.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

The engine stops because the computer does not recognize the new key. You must find a way to get the truck and technician with right equipment in the same place ( usually the dealership service ). I do not know of any alternative.

Automatic transmission ? Try moving gear selector to neutral ! Park neutral safety switch ?

This is more than likely related to the electric fuel pump or something downstream in the fuel system. turning the key on and wating a few seconds before starting allows the pump to pressurize the system. Might also be a bad fuel filter, but the key here is keying up and waiting and then a immediate start, that is what leads me to this solution.

Hope this helps.

I always key up and wait a second or two on all my vehicles, to pressurize the system, then turn the engine over. I have learned this is good practice with any vehicle I have owned..

Hope this helps.

catalitic converter is clogged up its not lettig the car breath

My son had something similar with his rav 4 it turned out to be the alternator which in turn damaged the voltage regulator try a recon alternator first you might get lucky.

I had same problem when I had a plain copy of the key made.
There's a proximity chip in the factory key or something, but the plain copy would not work. Engine would crank, then immediately stop. I didn't need the extra key bad enough to spend $80+ at the dealership.

Before you crank try and cut key on for 5-10 seconds then off and back on then crank if cranks up then you have a fuel problem. this will allow pump to run and pump fuel up. could be a bad check valve in pump causing fuel to drain back

Try turning your key on and off 3 times before you start the car, if the engine starts more quickly it means your fuel delivery system is not holding pressure and when you stop your car the gas at the engine runs back to the tank. You might also see if the engine will start immediately if you turn it off then restart right away compared to starts in the morning.
Gerry