1999 2.0i LS standard Vectra (black top engine). 12 months ago it had a run of misfires after about 10 minutes driving time. This cleared up, and it was fine for nine months or so, then the misfire returns, and the engine also cut is out.. Again after about 10 minutes driving time.

l have changed the HT leads and plugs ,which were rotten due to an oil leak. l have cured the oil leak too. It has a good air filter, it has been serviced recently and as an ex British Telecom Fraud department car, it was dealer serviced regularly before l came into ownership.
l have checked all the hoses, and replaced several that were on the way out. All the wirse plugs and cables seem to be in good condition with good contacts. All the fuses are present and good.

After a week stationary, it started and ran OK, but still with the misfire etc... After another week, the misfire was worse, and now... It wo not start.I am guessing MAF sensor, Lambda Sensor etc... Could be the problem, but l wonder if anyone could back that theory up, or if anyone knows better than l do about what might be wrong ?

The only known problem this car has is a leaking exhaust manifold at the cylinder head ,it is a minor leak due to a broken stud. It is also had a minor front end shunt, but it ran perfectly well after that, the only casualty was the air con radiator. (the air con did not work anyway)

Any help or even educated guesses are welcome. Points go to the most comprehensive answer.

Thanks

If u have an exhaust leak, l would probably work with that, l once had a car that misfired due to an exhaust leak, but then that happened all the time.
Also when u get a misfire is it raining or anything like that, as it could be water getting into electical contact.
l would recommend a fault memory check to be carried out, as it could be a sensor issue, but then u would not have to pay to have the part fitted, as u sound like u have some understanding, so u could probably fit the part yourself.