(G) It Lives It Dies it lives again

2002 Stilo 1.6 Dynamic. Starts first time dash says everything is o.k. then it drives for about 1 hour then cuts out. No warning just dies. When I try to re-start there seems like there is no power getting to starter. When I leave it for 15-20 minutes it starts again and then runs fine - for another 60 minutes or so.
I have fitted a new battery and a diagnostic check revealed no problems. One of the earth cables were replaced because it was corroded. The garage then handed it back saying eveything is fine. But guess what when I drive it it still cuts out and will not re start.
I get no warning and no warning lights come up on the dash. Could it be the key or immobiliser that is the problem. Has anyone else had a similar problem and if so how did you fix it? Seansaab

imobiliser is only to start the engine,, so if the imobiliser is removed or anything once engine is on that wouldnt matter.

overheating somewhere? and your thermostat isn't working?

When I try to re-start there seems like there is no power getting to starter.
Do you mean
The starter engages but acts as if there's a dead/ or low battery ie turns over slowly
Starter doesn't engage at all and nothing happens when you turn the key to the start position

Does it only cut out when you are at tickover or does it just die even at speed?

Engine just cutting out and not restarting for an hour sounds like an rpm sensor fault but if the starter doesn't turn the engine that's a different problem.

With engine running check the voltage drop between the battery neg and a good clean earth point on the engine, Should be near to zero, anything above 0.1v and there's an earth problem. Always a good and quick preliminary check to do

I know you've fitted a new battery but what is the battery voltage reading as this can show up a bad earth too

Immobiliser would not allow fuel or ignition to engine ie normally fast engine turning over but no sign of life and would give key code warning light

Overheating you'd see on engine temp gauge and lots of warnings and beeps

Hi Deckchair,

Many thanks for your thoughts.The car cuts out both at idle and when you are driving which is pretty scary when you are doing 70mph. Then when you turn the key to restart the engine it sounds like the battery is flat i.e. lights come on on the dash but the starter does not engage you just get a 'click' noise. Then when you leave it 20 minutes or so it starts 1st time with no warning lights and a notice of O.K. from the display.

The mechanic that worked on the car checked all the electrics this is how he found the corroded earth cable. Once that was replaced he could find no other problems.

There is no problem with overheating temperature gauge sits at 12 O'clock and the electric fan cuts in okay.

Could it be a problem with the ignition key?

Still sounds like an underlying bad earth problem

The fact you only get a click when you turn the key to start then I'd check the voltage drop between the battery earth and and earth on the engine

Easy check
Engine running, check the voltage between the battery negative terminal and a shiny good earth on the engine. You want as close to zero as possible and steady. Anything like 0.2v or above shows a problem is there

Your electrician also guessed a problem is there but i wonder if it is actually fixed now. It doesn't sound like it is