[Paul Sanderson]

Volvo S40-S (manufactured 2003)
Engine number: B4163358648

The Variable Valve Timing unit (VVT) on the top of the engine makes a very noticeable intermittent chuckling/grinding sound when the engine is at idle. We’ve replaced it with a new unit… but the same thing continues. When both units had the wiring disconnected the noise stopped (though when fired up again the engine did so easily and continued to run smoothly at tick-over).

This suggests that both the old unit and the new unit are in fact OK but were reacting to a bad signal coming from elsewhere.

The car runs OK otherwise. It’s only when the engine is under sudden load and the VVT is needed that the noise is apparent. Typically, this is when pulling away at low revs, and the engine is a bit jerky and likely to stall. One deals with this by raising the revs a bit and slipping the clutch, but of course that’s ‘bad practice’. During normal road running the engine seems OK though the higher engine revs might smooth out any imperfections and also mask any noise – so we don’t truly know if this is happening further up the rev range. I now take particular care to choose my gears carefully – in other words I avoid putting a strain on the engine… and that's how I should be driving anyway!

At the time that this became apparent we’d just had the catalytic convertor changed. The engine warning light is on but that was assumed to be because of the car recognising that the new c/c was not Volvo’s own c/c. The light can be turned off but comes back on again at about 3000 revs, so now the thinking is that it may be to do with the VVT circuit and not the c/c circuit.

Anyone any ideas?

Best regards, Paul Sanderson
sanderson-by-the-sea@hotmail.com