I have a 98 volvo v40 which is generally very reliable. However, for the past 2 years the engine start racing when idling or in 1st or 2nd gear and a lot of black smoke comes out of the exhaust. The only way to stop it racing is to put the car into neutral and press the accelerator or to depress the clutch very slowly. This has been happening only occasionally ie about once in every few months however I went on a long journey over the weekend and stuck in traffic on the motorway this problem kept reoccurring. When it was happening occasionally, I brought the car to two different garages but was told that they could not find a problem as it was happening only intermittently. Has anyone got any idea of what this could be please?
Thanks
Shermy