06 BMW 330i Stalling when comes to a stop, Fluctuating RPMs

Hey, i recently bought a 2006 bmw 330i from an auction, i drove it for two
straight hours from the auction to my house. The next day i get back to it and
drive it to the gas station to fill up and it stalled twice and the SES light came
on and it was hard to turn back on, i thought it may have been low on fuel so
filled it up brought it back home and later that night took the car to drive in the
neighborhood to see if it happpens again and it did only this time it would not
turn on so after trying for 20 minutes to turn it on i gave up and walked back
home. Next day went and jumped the battery and it started so i got the battery
replaced from a friend and the took it to a guy who works only on Bmw to
reprogram the battery, and he saw some of the vaccum pipes were not tight
and he tightened it for me and we both hoped that was the problem but nope
still the same problem and took it to another bmw mechanic to see and he
found no codes or problems either and as of today its still stalling, What I have
noticed is that the RPMs fluctuate between 1 and 0 and it shakes a little bit
and when it drops to about half way the SES sign comes back on and the car
restarts easily now after the new battery. But the car doesn't stall everytime
sometimes it drives fine so i have no clue and dont have a lot more money to
spend on it.