Punti 75SX cutting out and erratic tick-over

I have Fiat Punto 75SX. Which has always had erratic tick-over since purchased secondhand 3 years ago but it used to run well. The tick-over can vary from 500 to 2500 rpm at times and standing at traffic lights it sounds like an impatient driver.

However it has now started to cut-out and I've recently discovered (I think) that it's the petrol pump stopping. When cut-out occurs (sometimes whilst driving) it will not restart until you hear the petrol pump running after the ignition is turned on. Well, it sounds to me like the petrol pump I don't know what other gentle purring noise it could be.

There are so many sensors sending messages to the ECU that I'm at a loss to know where to start. A (non-Fiat) garage has suggested it's the ECU but they plugged their computer technology into it and it failed to even register the ECU was connected! They thought the ECU was getting too hot but I can't prove this. I've used the red key to 'reset' the ECU.

I know I could buy a second-hand ECU but if it doesn't cure it where do I go from there?

The car itself drives and runs great - when all's well. It has just passed an MOT and there are no warning lights indicating any problems.

A few questions...

1. I occasionally see ECUs going very cheap on eBay but can they be connected without something being done to clear out old settings from the previous car?

1. My current ECU is an IAW 8F.5T does anyone know if this the correct ECU for a 1996 N Reg Fiat Punto 75SX?

2. Am I on a wild goose chase thinking it's the ECU?

1. Or, is it simply a sensor controlling the fuel?

Any help will be gratefully appreciated.

Thanks

Rick