Engine cuts in low rev range then restarts and now its hard to start up

Hi

i am new here hope you can help me. 

I got Focus mk1 1.6 2003 last week 119500 miles on the clock full dealer service stamps till 2015 timing belt done at 94000. Car was driving well until yesterday evening driving from work I noticed it cuts then restarted and a oil or battery would turn then disappear quickly when braking but not when stopped however it idled roughly and sounds like a small diesel engine.

I have been to my mechanic (Indy)who said its probably bad petrol from Esso and suggested I get Shell V Power and blast on the motorway. I asked about the idle control valve and said its not it. He also blocked one of the air intake pipes on the engine and replicated the problem and blew into the pipes while disconnected from the engine but did not feel any blockage in the intake hoses.

On my way to Shell it turned off at the lights completely and battery light came on before oil and engine light. I restarted straight away no problem and drove home having decided to do the whole petrol business on my way to work later on as I use the motorway anyways. 

When it was time to go it cranked roughly, wouldn't start and starter motor would screech before it stopped cranking. I managed to start it by stepping on the gas while cranking and it woul rev normally till I left it to idle and when revs below 1000 then it would shutt off again, haven't touched it since after blowing my Fiats engine 2 weeks ago cos driving a car with a slight problem.

Any advice is welcome. Also no codes on diagnostic but when engine is off fuel and temp gauge go to half and work properly when engine is on.

Sorry for the novel.