assuming you already did all the regular maintenance required: change oil, spark plugs, clean/change air filter... if you can get access to an OBD scanner, you can check the LTFT (long term fuel trim) and STFT values of your car for any abnormally high readings. probably you have a "rich" condition. I've seen similar conditions without turning on the yellow check engine light for an error code. dirty/faulty MAF sensor and oxygen sensor can also cause this