320i missfire

[scs1]

I have a 320ipetrol coupe that was bought new in 2008 and is still under warranty. The car sometimes" Jerks" when pulling away and the engine sometimes missfires when in a high gear on a light throttle. It went back to the supplying dealer for this and a separate problem earlier this year. Whilst they acknowledged the "missfire" problem and said they had solved it (they had't ) they charged me £110 for investigating the other problem because they could not find anything wrong.
I have just booked the car into the same dealer to have another go at the missfire and they have informed me that they will charge me if they cannot find the cause. I have insisted that when I leave the car with them and before they open the bonnet that I will take a technician round the block and hopefully demonstrate where the problem is.
What I would like to know if any one knows if this is a particular fault on the 320i as I would like to turn up with as much ammunition as possible.
I forgot to mention that when the missfire is at its worst the yellow "engine" symbol lights up on the dash for a few seconds.
What I am trying to avoid is being presented with another bill when I go to collect the car.
Any suggestions would be appreciated

[roofer]

Sounds like an injector to me, if you have presented the car and they have acknowledged a fault, and not cleared the fault, they owe you investigation fee imo.

[phelix]

Is the car still under warranty? If yes how can they charge an investigation fee, at least first time out?

[scs1]

Had a long "debate" with a Manager of my dealer, Barons in Farnbough. He told me BMW UK will only pay for warranty work if a fault is found, therefore Barons were not prepared to cover any investigation work themselves even though the car was bought new from them . The only concession they have made under pressure is to hook the car up to the diagnostic machine free of charge . Any further investigation is chargeable. In that case I will be taking the car away at that stage and going to an independent, although I am confident a drive round the block with their technician will prove my point. They did admit that the problem is probably the injectors and as BMW UK instruct dealers only to replace two at a time,thats why the missfire was not cured first time round. Call me cynical but what is there to stop any dealer replacing a part under warranty ,claiming the cost back from BMW UK then telling the customer that no fault could be found but "it seems to be OK now" and charging the customer an investigation fee. The car goes to the dealer in a couple of weeks I will let you know the outcome.