hi, I was viewing a vauxhall astra, 1.6 litre which just had its mot done a month ago which it passed. The owner turned the ignition key, and the car suddenly started to rev upto 4000, without even touching the accelerator pedal. We waited for 5 mins and turned the engine off, and did it again. It was okay, but then when driving it started to rev again. The car keeps on suddenly revving up. The owner did say that he hasnt driven it for a month, and mot was done last month. Its the first this has happened according to him. What could be the problem and is it worth buying it at £650?