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I recently had a major service on my 2000 Subaru Legacy including water pump, cam belt, new plugs, oil & filter change and intake valves cleaned ($2k and 12hours labour all up).

The engine now has a surge when idling mainly when the engine is cold and this becomes even worse when the A/C is switched on.

I took it back to the workshop where I was told it needed a good "drive".

Have taken it for a 2 hour drive but it is no better. Any ideas?

Another problem is a slight knocking noise from the front suspension at low speed.

I am finding it hard to get reliable information from mechanics!

Jacob

From the "Ask Jack" archive - 11 December 2009

If the mechanic is telling you the car needs a good run after all that work and money spent, then I would have to question their ability to be honest.

While I cannot tell you exactly what the problem is, I can say for certain it is a waste of time continuing to drive the car in the hope it will improve. One possible reason is an air lock in the cooling system causing the temperature sensor to read erratically.

I am also intrigued about the intake valves being 'cleaned' during this service. Not sure what you have been charged for there to be honest.

Take the car back and tell the garage to sort the problem out (I assume the car was fine before the service / cam belt work). Bypass the mechanic and ask to speak to the business owner or most senior person on duty.

Make the rough running your first priority and worry about the slight suspension noise later.