Toyota Repair: 2000 toyota corolla ce 1.8 liter in line 4, mass air flow sensor, mass air flow

Question
hello mike! my question involves my girlfriends 2000 corolla ce 1.8 liter in line4.(aprox.67,000 mi.).about mid june the car was experincing starting and hesitation symptoms while the check engine light was on. i took the car to my mechanic here in henderson nv. and he said the scanner showed that the mass air flow sensor needed to be replaced and the job would cost over $500.00. i gave him the o.k. and on aug 25th my g-friend drove to phoenix  visiting her mom and the check engine light turned on during her trip and she took it to moms mechanic  who said it was the coolant sensor and that the mass air flow sensor job should have cost only $300.00+ . i have been going to my mech. for 2+ yrs. and no shady tactics so could you possibly tell me if my mech. was just?  p.s mech. in phoenix could be on d-fensive cause my g-friend had complained about poor service of his for many months but her mom has a barter deal with mech. and is stubborn. (sorry quest.was so long)  

Answer
I need to know what the code was to be sure.

A po171 would indicate the MAF if the fuel trim readings were high on the freeze frame data.
The coolant temp will give you a different code and is unrelated.
However
P0171 is a "lean " code. If the coolant temp was incorrect and the engine trys to compensate for a temp that is false, it may alter the fuel trim and thus give a "false" MAF sensor code. I would do the coolant temp sensor first. Then see how it runs.



Mike