my daughter has a 2001 v70 wagon. it has been a good car for her since she bought it used a couple years ago. it has been showing a check engine light for a while, she said someone checked and said it was an o2 sensor, i know that someone and i would not count on that as gospel. anyway, car ran fine until a few days ago. then the check engine went to "urgent", and the car ran with no power, 2000 rpm max and about 5 mph max. shadetree mech dad looked things over, found the dirtiest aircleaner ive ever seen, blew it clean with air hose, voila, back to check engine light and a good running car. not for long. a 20 mile ride home, worked well for 19 1/2 miles, the last half mile it went back as before, and it crawled into their yard. i went up there, looked at it, pulled the air cleaner entirely, and it ran good again. that after being shut off when they got home. i told them go to the store and get a new filter tomorrow. when it started, it ran crappily again. by the time i got there, 1 hour, it started and ran fine. when they tried again this morning to start it to go get the new filter it was crappy again. i put a code reader on it the very 1st time, but a cheap code reader. nothing. i am going to borrow a good reader and try again. any advice is appreciated, PLEASE!

thanks
ken