2001 Mitsubishi Montero Problems with engine Idle

Hi, hopefully you can help me with this. I have a Montero Sport 2001 with 148k,
I would drive the car normal for like 30 minutes then I would park the car all fine, then after 10 minutes I try to start it, the car turns on but after 3 seconds it shuts off, if I keep a foot on the accelerator the car will remain on but as soonest I release the gas it will shut down, so I have to wait for it to cool down then it will work normal, that started happening 2 weeks ago now the car has a new symptom, If I'm driving over 40 mph and I stop maybe for a traffic light or an stop sign the car would shut down, then I would put the car in park so I can start it and it starts right up with no apparent problem.
I took the car with a mechanic and he has no idea what could be, I bought an expensive additive to clean the fuel system and it did not worked.
Thank you!