I have a query on a 1995 525 TDS which appears to "misfire" on one cylinder when hot - it sems to start and run smoothly from cold but after a few minutes the idle becomes "lumpy", as if a weak cylinder or misfiring. It pulls away again apparently normally, not "misfiring". The car has been driven only sporadically over the last few months / done very few miles
- I don't think its "mechanical" like a burnt valve, or cracked piston rings as it seems smooth on a cold start up, but come up to a junction after a mile or two and it seems to be missing on one cylinder, although pulling away again it seems normal.

Anyone any suggestions as to what this might be ?

Thanks,
Nick