Limp-mode at idle?

I have a 2004 Nissan X-trail 2.2 dci, which goes into limp-home mode if I let the engine idle for two minutes. No fault lights are coming on. John Gallagher

If the engine is going into limphome mode, the ECU should record a code. This means that the problem may not be the engine actually going into limp-home mode, but that it is running so poorly it appears to be in limp-home mode.

Although this may seem to be splitting hairs slightly the important point is that if the engine is not being put into limphome mode by the ECU, no subsequent code will be left in the system.

Working on this theory, one problem that Autodata tells me is a common issue on your series of engine is the fuel control valve. This will cause various problems including loss of engine revs, poor starting and intermittent power loss. The remedy is to fit a new fuel control valve in the high-pressure pump.

Failing this, the best method of diagnosing the fault would be to use a scanner that can read off live data; this should show up any areas of concern.

Diagnostics Doctor is a FREE helpline service for CM readers – including trade readers – who are struggling with diagnostic/engine management related faults. Steve Rothwell will answer all your queries. He will need as much detail as possible:

MAKE, MODEL, YEAR, ENGINE CODE and NUMBER PLATE of your vehicle – and the type of management system installed. Obviously, Steve will not be able to assess the vehicle up close, so his answer will be on the basis solely of your description. This is a FREE service and it may take some time to respond to certain problems. If you would like to receive a personal response via post, please enclose an SAE.

Write to: DIAGNOSTICS DOCTOR CAR MECHANICS BAUER MEDIA, MEDIA HOUSE LYNCHWOOD PETERBOROUGH

PE2 6EA e-mail: cmdiagnostics@yahoo.co.uk