Vauxhall Astra occasional intermittent loss of power whilst engine running

This problem has only been occurring occasionally, but has recently happened more frequently. For example, I'm standing still at traffic lights and when the lights change I go to pull away but when I depress the accelerator pedal the car has no power and barely moves.

If I take it out of gear (it's an automatic) for a moment or two and then put it back in gear it will then usually pull away more or less normally.

On a recent motorway journey, there were occasional moments when the car seemed to lack power, although it continued running. It felt as though if I had tried to accelerate to a higher speed (I didn't) it would not have responded.

Generally, the car starts very promptly and ordinarily runs very smoothly. Apart from the problem described above I'm very happy with its performance.

I've had a suggestion that there is a solenoid somewhere on the car that might be faulty.

I'd be grateful for any suggestions as to the problem or any reports from other owners who have had similar difficulties.