I may as well start from the start so everything is here!

My car was running perfect until I had to change my reverse light switch. So out came the battery and the intercooler.
Once all put back together, I was aware that the ECU had to be reset properly (as it had been out for more then 30 mins) so i did that.

Ever since I have had a dodgy idle, occasional starting problems and can sometimes cut on when stopped at junctions.

I reset the ECU again just a few days after the 1st time and still no difference.
Now, about a week later, the engine management light suddenly came on and I am getting fault code P0171 on my scan gauge.

I am certain its all related as it was perfect before the battery and intercooler came out. But could it be possible its just a coincidence?

The reading is meant to mean its running lean? However since the light has come on the car has a stong smell of petrol!

Any ideas what this could be?
CheeRS