Vauxhall Corsa power loss at approx 3000rpm + engine management light on. light goes out when revs drop

The car drives OK up to the point where you accelerate beyond approx 3000rpm then suffers a power loss and the ecu light comes on. The light goes out when you let the revs drop. There has been some idle fluctuation but this is not regular and does not cause a problem. Car starts OK. Tried to read fault codes by bridging the terminals in the diagnostic port as per Topbuzz web site but no joy. There does not seem to be a terminal in the position required.

Engine code is X12XE if this helps.

Any help would be appreciated.