m420m

When I start my car(not all of the time just a time or two every week or two) it struggles and stays around 500-1k RPMs, then dies. I took it in and they replaced the spark plugs,a coil pack, and the plugs on the battery. But it still seems to struggle, until I rev it up a bit and shift into reverse and go, and it is fine from there. Any ideas why thins is happening/ what to do?

Thanks for your time