I have a 2001 V70 T5 manual with 145k miles that I've owned for almost 2 years now. Since I've owned it I've noticed a slight hesitation or "lurching" under full throttle between 4-6k RPM. It's barely noticeable to most people but drives me nuts.
In the last couple months I've replaced all the coil packs, spark plugs, and air filter. I always run premium gas and there's currently no engine check light.
Last week the check light came on (P0456 - small evaporative emissions system leak). I reset the computer using an OBD2 reader and for the first hundred or so miles, the slight hesitation was gone and the car made noticeably more power. Now the hesitation is back again (no check engine light).
Any ideas on what I should try next? I was going to try cleaning the mass air flow sensor to see if that fixes it. Could these symptoms be caused by a failing ETM? I've noticed some occasional idle fluctuations... I've read that this could indicate my ETM could be on the way out. Any advice would be greatly appreciated. Thanks