error code

P1131 means the bank 1 Oxeygen sensor indicates your engine is running lean (not enough fuel). Bank 1 is the cylinder head in which #1 cylinder is in, in your case you only have one bank being a 4 cyl, in the case of a v6 or v8 these engines have two banks, bank1 and bank2. Any how one of the most common problems with this car is a dirty mass air flow sensor or vaccum leaks, but as stated you believe it doesnt have a leak, I would get some approved MAF cleaner and clean it, clear codes and go from there.