Car starts but it's cut off if I let off the gas pedal
 

My 2008 Hyundai accent takes long time to start and once I get it to start it will cut off if I let go of gas pedal but it's struggle to get it to start
I can't get any codes on the scanner

I would suspect there is a good sized vacuum leak.in the intake system.
Look for a hose that might have come off, cracked or broken.

You should be able to tell if there is a big vaccum leak easily with an OBD reader by monitoring the Manifold Absolute Pressure (MAP) sensor. When you are idling you should be around 30 kPa. When you are at Wide Open Throttle the pressure should be close to atmospheric pressure (e.g. 99 kPa). If you have a big vaccum leak you should see MAP significantly higher than 30 kPa when you are idling.

I'd be curious what you end up finding, as I have a pickup truck (2012 Silverado 4.8) that has a similar issue (sputtering start, needs throttle for cold start) and it has been very mysterious so far

Hi Raphael,
I agree with your logic, however , not too many folks have the equip to do the checks.

When an engine will not idle unless you depress the throttle pedal most times as the throttle is depressed more air is allowed into the engine and the computer gets that info PLUS throttle position and increases injector on time = more fuel and the engine runs fine. With that in mind , we start looking for an intake air leak (vacuum leak).
What do you think ?

OP had mentioned he has a scanner so he could look at MAP (altho we are assuming the sensor is giving good values with that approach)

I am sure your logic is sound - I don't have much experience, just mechanically inclined and I had a similar problem with my truck - but it's not fixed yet so what do I know, really XD. In my case though the truck doesnt just die if i stop giving it some gas. Once it warms up it steadies out, after only a little bit of hunting while its cold. After it stabilizes for a few minutes you can shut it off and restart no problem.

Maybe,,,,, two considerations.
If there is a vacuum leak, that as parts get heated they expand and close the opening , so the condition improves.

If the battery has been disconnected , a lot of learned memory in the vehicle computer gets lost.Then when we start it , naturally we step on the throttle so it will not stall and the computer learns that move. Something you might try, start the engine not do not touch the throttle and it should program itself for the correct idle speed and fuel mixture.
It is called a relearn procedure and usually works if there is no vacuum leak.

Hi Mik,

Do you have a scan tool , not a code reader, but a scan tool ,to connect to your vehicle ?