stalling

Hi Everyone, I was hoping to get some advice from anyone kind enough to offer. The Car 2005 Astra H 1.7 engine code(?) is Z17DTL The problem: The engine starts and ticks over for a few seconds at normal idle rpm. Whilst still stationary, the revs then drop slightly at which point the engine...

Has been through diagnostic test which shows no issues. No instrument lights illuminated. Car feels as if trying to pull away in third gear when in 1st. Need to keep revs high 2-3000 or feels will stall, especially if starting up hill. Gradually getting worse. Feels as if lost its injection...