Really need some advice, I purchased an 04 plate A4 1.8t Quattro (190) from a dealer in november. After the test drive (which was fine) i insisted on the car being left to tick over whilst having a second look around it. After around ten minutes it developed a very slight squeaking noise from the engine. The dealer agreed to have a garage look at it so i gave a deposit and returned 2 days later to collect it. The dealer provided a labour reciept from the garage and explained that the guys at the garage couldn't get the car to make the noise but they thought it was a dry pulley bearing and so they had greased the pulleys and that should be that. I took the car for a second test drive and again left it to tick over for about twenty minutes and there was no sign of any noises and so i took the car on the condition that if the noise returned the dealer would sort it at his expense, and that he upped the warranty from 6 to 12 months. To which he agreed.
The car was great for about three weeks but then the sqeak returned, I phoned the dealer straight away and arranged for the car to go in 3 days later. In the meantime i tried not to use the car but being on-call at work ment it was inevitable. The day before the car was due to go in the sqeak developed into a harsh sqealing noise, which further developed (after about 4miles) into a scarily rough idle and an even scarier engine management light. I pulled the fault codes from the car that night and it only showed P0171, looked into it and found out it was probably a split hose or valve. I explained all this to the guys at the garage the next day and it turned out to be a plastic valve at the back of the block which had cracked, they replaced it, and once again the car was great no problems whatsoever.
Over the last few days though the sqeak returned and last night it started running like a pig and the engine management light is back, along with the HUGE sqealing. The fault codes this time again shows p0171 but worryingly it also shows p0301 and 302 which translates to a misfire in cylinders 1 and 2.
I emailed the dealer last night to explain and asked him to book it in, but i don't know how to go about things because i have lost all faith in the car. The sqeak and idle problem must be related and the fact the problem has occured twice in two months leads me to believe there could be a serious underlying problem. I will call the dealer in a bit to have a chat but i don't know whether to just demand a refund or give the car the benefit of the doubt and risk giving it a third chance. This is the first time i've bought from a dealer and could do with some advice on my options and any technical advice that may be out there.
Thanks for reading
Any help very gratefully received,