My car never used to do this before, but ever since my battery went flat because I left air con button on and interior light on, after jump starting my batt, every time I start my car now I need to floor the accelerator lightly to get the car to start up and run whereas if I didn't press the accelerator, the revs would fall off and stall. There's no change to the way it drives and is only on start up. Before I just turn the key and would start fine. Any reason this is happening?