I have a 2002 Cooper S

My idle sits just under 1000 RPMS, which likes to bogg out and sound like it's going to stall. This has been recent over the last couple weeks following its hesitation to start in the morning: Every morning it turns over a bit slow, then starts, but struggles and dies out almost imediately. Sometimes I can save it by hitting the gas, but the 2nd start-up always works fine. I just started feeding it seafoam and lucus injector cleaning additives to the fuel, but wonder if there is something else going on that someone has any insight on. ?

BTW, I know I go up and down some hills in my area when driving, but does 20MPG sound a bit low? Maybe it's all part of the same problem?