i have a code P0172 put new mass airflow sensor what can it be

P0172 Fuel System Too Rich (Bank 1)Possible Causes Setting Conditions •Base engine "mechanical" fault affecting one or more cylinders •Check for a restriction in the air intake system (e.g., a dirty air filter element) •Check for a restriction in the Exhaust system •Fuel delivery system supplying too much fuel (e.g., leaking pressure regulator) •Fuel injector (one or more) leaking fuel •HO2S has failed (it may be contaminated with fuel, silicone or water) Engine running; ECT signal more than140ºF, estimated altitude less than 8,000 feet, estimated canister loading less than -15%, fuel adaptation less than -27%, and the PCM detected that the Bank 1 Long Term fuel trim (LONGFT) was less than -17%. The PCM monitors the HO2S signal and then adjusts fuel delivery while in Closed Loop. Changes in fuel delivery will be indicated by the long-term and the short-term fuel trim values. The ideal fuel trim value is near 0%. The PCM adds fuel when the HO2S signal is indicating a lean condition. Additional fuel is indicated by fuel trim values above 0%.

running to rich. fuel pressure regulator, injector, clogged air filter. if a shop did this repair, have them re check there work. Roy

I agree with Roy. "clogged fuel lines" will not cause this problem. It appears that the shop that did the valve cover gaskets isn't looking closer at the work they did. Think about this, you didn't have this problem before they did the valve cover gaskets.

Did you ever resolve this problem?