Vauxhall Zafira lose power when accelerating

Originally my car wouldn't start when the engine was warm unless I kept my foot on the accelerator and put it into drive whilst pressing brake too. Once it was going, the idle speed fluctuated at traffic lights or in slow traffic and often cut out unless I kept the revs up. Tricky with an automatic in the town centre! However, I've just changed the driver's side rear brake caliper and the car has sat on the drive unused for a few days whilst this was happening. Took it for a test drive today and now the opposite is happening. The car starts even when warm but get up the road and the engine cuts out completely. The engine management light is on permanently. I change the air filter last week,I've recently had a new lambda sensor about a month ago and six months ago had a new air flow sensor. I was going to get the EGR valve cleaned until this problem arose. Could it still be that? Or is it connected to changing the brake caliper?