Misfiring problem

[Ray22]

I have an Audi A6 Avant, have owned it for about 5 years, 2003 1.9tdi. 216000 miles. After starting from cold it runs fine for about 2 or 3 miles then miss fires under load for a few minutes, the ESP light usually comes on then it is very uneven. I switch off and restart, let it tick over and off I go, sometimes I have to repeat this straight away then off I go with no further problems until it starts from cold again! Audi garage checked diagnostics costing over £200 only to say they didn't know what it was but suggested it could be the head and considertha car age and mileage was not worth replacing as it would be expensive and put additional strain the rest so causing further problems. Injectors have been suggested along with the head as above but I thought the problem would be on going if this was the case and not just whilst warming up. A frustrating problem. Any thoughts as to what it could be or tests I could carry out would be greatly appreciated. Thanks Ray

[nemohm]

As previously mentioned we have no experience with diesels here.
Sorry,