If the engine light for my st170 is on caused either by the imrc or lambda sensor fault will it cause any damage if I keep running the car? What would these faults actully'mean' for performance/fuel consumption etc?

Or if no one knows the answer, has anyone ran theirs for a while without any (further) problems?

depends on what the actual error is. the engine light is the same thing as saying 'my computer has an error'. it might be fine for years or the engine could blow up in 5 miles.

If it was either a Lambda sensor or IMRC fault?

I ran mine with engine light on for a lanba sensor problem for the best part of a year without any real problem. Then the performance started suffering and the fuel consumption shot up which was a blocked dpf so I have that fixed by taking it all out and deleted on the ecu. The guy who did the work showed me that the sensor tubes had been burned through and so this had been causing the faulty readings all that time, but they are now redundant and deleted from the system.

In hindsight I should have taken it in earlier, if only to put my mind at rest - I do regular long trips and the last thing I need is an unscheduled stop on the hard shoulder of the motorway. I think a new lambda sensor isn't that expensive, at least not on a diesel.

I have a Honda Accord with the EML light on, has been for approx 2 and a half years. The lambda sensor failed, and a generic non-Honda part replaced it, but the EML stayed on. The car has been running fine. I don't know though if I would run the gamble on a ST though.

Sent from my telegraph using Ford OC

Generally speaking, if it's orange get it checked, if it's red don't drive.

It's the orange warning light that comes on. It doesn't seem to affect the running of the car and it's doing an average 31ish mpg. The light goes out for 300 miles after the battery is disconnected but then comes back. It also sounds as if there is a slight rattle on the exhaust. I'll get it checked out next time the light comes on just to be safe.