Computer reset...WH2 Stato

[SLIfox]

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.

 

[BlackVXGTS]

The instructions below are from the VT/VX Service Manual. However, they are very time consuming, and I think most people just drive their cars normally and the learn procedure works itself out over a couple of days of driving.

IDLE LEARN PROCEDURE
Whenever the PCM or the battery is disconnected or the PCM loses power, the PCM’s learned position of the IAC valve pintle is lost, resulting in an unstable idle.
Perform the following procedure in order to return the IAC valve pintle to the correct position:

Automatic Transmission
1. Turn OFF the ignition.
2. Restore the PCM battery feed.
3. Turn OFF the A/C controls.
4. Set the park brake and block the drive wheels.
5. Start the engine.
6. Shift the transmission selector to D (drive).
7. Allow the engine to idle for 10 minutes.
8. Turn ON the A/C controls.
9. Allow the engine to idle for 10 minutes.
10. Shift the transmission selector to P (park).
11. Allow the engine to idle for 10 minutes.
12. Turn OFF the A/C controls.
13. Allow the engine to idle for 10 minutes.
14. Turn OFF the engine for 30 seconds.