I tried to install a performance chip in my 1991 325i bmw and I messed up the ecu, its model number was 0-261-200-525 so I bought another ecu with a model number of 0-261-200-173 and has a stock chip in it, but its running better. What I want to know is WHY???? I know its not a bad thing but this info will help me figure out what type of performance chip to buy and so forth. Oh and I'm new to the site just fyi. So any input would be great, thanks.