Poor idle and engine stops when trying to increase revs.

I should have joined the forum a while ago but I'm here now and am looking for some help please.

I have owned my Tigra 1.8 exclusive for about 6 years and don't use it a lot which means it stands for a long time with the battery disconnected.

On Sunday I connected the battery and it started first turn of the key and was OK whilst I held the revs steady at 2000rpm. However when I took my foot of the accelerator it had a lumpy idle and when I tried to increase the revs again the engine stopped. I tried again and this time I was able to increase the revs but on third and fourth go the engine just died as previously. Fifth attempt was OK and I moved the car forward about ten feet forward to clean up a years accumulated muck off the pavement underneath the car. I was able to drive it back to the original position and called the RAC.

When the guy arrived he couldn't get it to idle at all so plugged in a diagnostic but no faults came up. He hit the engine ECU with a spanner and it all seemed OK. But after tturning it off and back on it started again but it wouldn't idle, the same as before.

He seems to think the engine ECU is faulty and needs repairing or replacing but I'm not convinced.

Any ideas guys?