Mufflers repair service near Gurnee, IL

Rating on Carx, Schaumburg, IL: Poor Diagnosis, Manager is very rude and no guarantee to the parts and labor even if the same problem occurs in next two days. Please don't go to this shop, If you get check engine signal. actually I could rate this shop zero star. Now a days These CARX guys are cheating customers. The manager Bill always gives high bill. Don't believe their free diagnosis test. They don't find real problem, rather they fix some thing and if the problem comes back again even in next couple of days, they don't help on that. Here is my story. I have been going through this CARX shop for since last 4 years. In the year 2008 and 2009 this CARX mufflers were really good. They always help to customers to fix the car problems with less price and with 99% guarantee on the work they did. After this new manager name Bill came into Schaumburg, CARX, this shop became like cheaters shop. Recently I took my Toyota corolla car to fix check engine signal. they did diagnosis and said code P0171, that means exhaust or lean engine problem..blah..blah. Then I told them, I will come back in 2 days and I did same. I dropped my car to fix check engine signal, This time different mechanic in same CARX and he said he saw different code with computer and replaces throttle sensor and other...and they gave me bill $588 for check signal ($330) and AC recharge. ($158). After I drove 50 miles, check engine light came back. I took car to CARX again. now this same mechanic who repaired it said that he is saying code PO171 that is the same one their other mechanic told very first time. This guy did something again and said fixed. After I drove 25 miles, check engine signal came back. I called manager Bill for same. He told that his mechanic is out of town and he asked me to comeback after 2 weeks. Then I took my car to carx on 08/12/11 friday, This time mechanic is there. Now the drama started. They simply said that, they can't determine which is causing PO1