I changed the battery on my car roughly 3-4 months ago.
About a month after that I was waiting to pick a friend up and whilst my car was running idle the engine management light appeared and the car began to run really lumpy. On the short drive home it felt like it was misfiring and got really jumpy when i put any real power in the throttle.
This problem came and went completely irregularly. Sometimes it would run absolutely fine and other times the EML would pop up and I thought the engine was going to completely give up on me! Every time the problem occurred the engine light would come on and the same issues would occur, it would run lumpy and began to kangaroo whenever I put any real power in it.
I took it home from university (a five hour drive) and it drove absolutely fine. I did some other work on the car such as cleaning out the starter motor because it was making that noise that is common with MkIVs on start up.
To tackle the problem with the engine light/misfiring I changed the water temperature sensor for an aftermarket one thinking that that would solve the issue. This did work for a period of about a month, but then the problem came back. Because changing the sensor had seemed to work before i presumed that, because it was aftermarket part, maybe it had just broken, so i got a genuine VW temp sensor and put that in, but it hasn't solved the issue.
Obviously the temp sensor isn't the issue, leaving me without a clue of where to go next.
I'm beginning to wander, as some people on other threads have suggested, that it's got something to do with having a new battery put in.
MKIV Golf 2.0 GTI 8V AZJ 115
Any ideas on resolving the issue would be greatly appreciated!