2000 Volvo V40 Will not rev. Much.

Please help. Car starts fine but once into 3rd or 4th or 5th does not want to rev, no power a job just to keep moving. Two mechanics had a look first sent it to the second as he did not know. Second put it on a diagnostic which just gave a quiry, for the fuel power sensor. Advised to blast it in second to clear dirt or new sensor, to me of no knowledge makes no sense one contradicts the other. At rest car idles at 2000 rpm, will not rev past 4000 revs, drives as if choke out full all the time down to 14 mpg. I know there is little straight in life any one suffered same or similar. Thanks Steve.