my wifes 01' C320 ck. engine light came on again and this time P0173 bank 2 fuel trim, some times it will bog down and die or some times it recovers and smoothes out. Reguardless it still doesn't have the zip that it has always had. Cleaned O2 sensor , 94 octane today. Any ideas would be helpful. I am suspecting MAF. But not sure how to confirm.