Help needed with a 440

I've had this problem for couple of months now.Hope someone can help. The car starts ok and runs at 1000 revs picks up to about 2000 then drops down and cuts out. When driving as soon as I take foot off accelerator,slow down and brake it cuts out. Also while driving there is no power, like when I want to go above 30 the car stays at 30 when I put foot down then the speed just shoots up after few seconds or it cuts out. It's a 440 1.8i, I've just put a new battery in it and that hasn't made a difference.

Look for air leaks . Has this prob been getting worse over time or has it been the same from the start?

It's got worse the last month, I've had a mechanic say he couldn't find anything wrong with it, then I've been told it's the clutch or fuel starvation. Will check for air leaks. Thank you for your help

Check the exhaust as well because when i had my 440 it became blocked and would only rev to 3000rpm. If it is the exhaust it will get worse until it will not run at all. Have fun Bob....