ive just brought the car and was told i needed a idle valve,but when i took to a garage they reckoned the valve is fine? they suggested that it might be the lambda oxygen senor? when its unplugged the revs stay down on idle and runs a bitbetter? would a faulty oxygen sensor make the revs go up and down and make the revs stick some times? cheers

 

The O2 sensor registers lean or rich conditions in the exhaust. If lean it tells the engine to add more gas, and vice versa for rich. So you could have a bad O2 sensor and it could ide the engine up.