Hello, so I just bought a used 2004 STI off a friend of a friend. I was out of town for a while and when I get home I start taking a look at my car to do any work that needs to be done.
well, first thing I notice is that the car was idling low around 400-500. (wasn't doing this the day my wife bought the car). the battery was dead for a couple of weeks so I replaced it and I was thinking that maybe the car was relearning. after warmup I press the gas and there is a little delay...the rpms drop to about 100 or less and the car stalled a few times. (if I press the gas enough the car wont die, obviously, but the rpms drop as soon as I let go of the gas. then it was struggling to get back to a stable idle) I added new gas and cleaned the MAF sensor thinking maybe things were dirty. So it felt like the car was getting stable after a full day of cleaning, test driving, etc. Then I changed the spark plugs last night and the idle went back to dropping to around 100-200 after I touch the gas pedal. The RPMs drop that low when the car is coming to a stop as well. I even stalled at a stop light and I tried to slowly move forward (the whole touch the gas pedal and the RPMs drop thing)
Now I am thinking that since I removed the battery it has something to do with it (it was twice that the car was reset and both times same issues)....or maybe my plugs weren't gapped right.....or maybe there is something else wrong with it that I need to look into. I also noticed that when im driving the car, it doesn't respond right away and feels like the delay I was talking about earlier.....(when im in park and I step on gas and the car drops rpms for a second or two) but it feels good in between gears when im moving fairly quick.
I am also reading -20 vacuum on my boost guage at idle.
COBB Accessport with custom tune ( I don't know how to use it yet but if I have to make changes then ill get some help )
like I said, my wife and friend didn't mention anything about it when the car was bought so I am assuming it was fine. (my friend would have told me something) any help is appreciated! Thanks guys.