How do u know when the mass air flow sensor is bad?? My 98 infiniti is hard to on 1998 Infiniti QX4

start. can be going down hywy and car will slow down and at times want to stall while holding the pedal at same speed.I can give more gas and let back off several times and it will clear up most of the time. the code is a p400 misfire code. i have replaced so many sensors, tune up, rotor cap and button, pcv valve,relay sensor.ANYBODY HAVE AN IDEA WHATS GOING ON???????

Asked by for the 1998 Infiniti QX4
This code is probably related to exhaust gas low or non-existent through the EGR valve. Need to check EGR for proper function as well as hoses and harnesses connected to it. You can remove the mass air flow sensor and clean it with MAF cleaner if you wish to do that as well.