impalaman

Greetings all. I know this is a common problem but my check engine light remains on. I initially checked the codes with my scanner and obtained P0170 and P0173. I replaced the MAF and cleared the codes but the check engine light
continues to come on and stay on and I continue to get the P0170 and P0173 codes. This is a 2000 E320 wagon with 137,000 miles.

The car runs well but I don't think my mpg is as good as it used to be.
The gas cap is original and appears to seal well.

Can anyone provide a list of possible causes so that I can troubleshoot?

Thanks