My 1991 300SE has been stalling lately. It will shake when I start it after it has been sitting. I will let it warm up a bit. When I have to stop at a street light it will stall, but it will start right back up. When this happens, I will take it on the highway and drive it around 70 mph for a few miles. Once I do that, it no longer stalls at street lights. But then after it sits for a little while, the process starts all over again. I did get a tune up about 2 years ago. I have a second vehicle and do not drive this car all that much. Any thoughts on what might be causing the shaky starts and the stalling? Thanks.