My WH2 statesman was without a battery for a month and a bit. Got a new battery and installed it now car runs a little rough on idle ,and wants to stall when you take it out straight away, but will get better within 2 minutes then runs almost perfectly after that sometimes feels like it wants to stall while stopped at lights. However computer says fuel is chewing at 20-40L/100km and then go down to (3-10L/100km) when I accelerate. When shifting gears it will completely reset to the 20-40L/100km. So confused any ideas would be great. TIA Ps will clean throttle body don't know if that will help anything though.