I own a 05 STI, when i start her up in the morning idle is good everything runs smooth up until she warms up. She then sputters as if im running rich, their is a burning smell and white smoke will come out of the oil cap when i open it. Ive changed oil (full synthetic), spark plugs, and gave her a full injector cleaning solution (probably why she smells funky). Now throughout the day, it has become more of a challenge to start her up. Id have to wait for my sti to kick over and apply small amount of gas just so she doesn't bog out. Any suggestions? ive read up that it could be my Coil Packs and Piston rings, still does that have anything to do with her starting up?

 

Hard to start car may need a new fuel filter. Or fuel pump or regulator is going out. I know it keeps fuel pressure higher until up to temp then drops it, which could be the issue. Have you done compression check? How many miles on motor? Have you checked valve clearances? A tight valve will misfire too.

 

Get a compression check. I was in a similar situation and my cyl 4 is toast

 

Get a compression check mines was throwing out misfire codes as well turns out to be a bad coilpack

 

Make sure u clear codes first then Swamp the coil from cylinder no 1 to cylinder no 4 see if misfire follows to no 1 if it doesnt and stay still at 4 next step would be take the compression test reading if it came low in compression and u still want to know more bring the no 4 at TDC and do the leak down test if the air is heard escaping from the tail pipe u got a bad exhaust valve if from the intake u got a bad intake valve take off the oil cap if the air heard through the crank case that means u are f u k ed bad rings good luck son