check out sears. i bought the actron pocketscan for $80. it was well worth the money at the time, as my '01 pahtfinder was throwing 3 different codes at the same time.
you can probably find them cheaper elsewhere, like ebay or craigslist. but here is the link to see what they are.
http://www.sears.com/shc/s/sea...=find
the code reader comes with the book and software to install and look up almost all models. it won't read my BMW, as that is a differnt port.
"bogging down " symptoms could be the usual suspects with our cars like,MAF, VTC solenoid and / or sensor .
if you don't want to spend the money, go down to your local pepboys or whatever you have and they should read your code for free.
good luck