2004 hyundai sonata, had engine replaced spring 2009 (belt broke, destroyed engine… salvage engine). This year, “mass air flow” replaced twice in June, again on Monday and engine light came back on after two starts. Difficult to drive car effectively because out of stops or up hills it often feels as if it is dying out (“give it more gas!”) 
and it often has trouble shifting into (could be out of?) 3rd gear - at which point he bumps it to “manual” mode and shifts then back to automatic. What are we missing?
I hit send before adding - it has been mentioned that if the service center is using after market parts, this could just be a repeat failed item. true?
I have to presume that your check engine light is on and that you have some error code that refers in one way or another to the MAF. There is no code, however, that tells you that a MAF is bad. The MAF is one part of a system and it is the system that has to be diagnosed.
What is the exact DTC code (P####) ?
Are You Replacing MAFs Based On DTC Codes After The Engine Light Illuminates ?
What are the weather conditions like when you’ve had this problem ? High temperature and humidity ?
Is this likely on a cold start ?
I don’t know if you’ve got a 2.4L or 2.7L engine, but you might want to check with a service facility / mechanic that has access to Hyundai Technical Service Bulletins. There are some that describe the procedure for updating the Engine Control Module (ECM)software to correct MAF / hesitation problems for 2003 - 2005 Sonatas.
It might be software, not hardware.
CSA
I do not know the exact code, but we’ve been told each time that the MAF code comes up. It’s been checked at All Tune (June) then dealership last Th, We returned to all tune because their work from summer was under warrante for a year, Both the dealership and all tune said the primary code was MAF. I do not yet know today’s code, but the engine light came on Tuesday morning (repair was Monday), no fuel fill up before light came on.
Weather has varied from hot and dry, hot and slightly humid (we’re in NH) to rainy. Our car is in a garage at night, insulated so it is warmer than outside in the winter and cooler in the summer. I’m not sure on the engine either, but it runs like our little elantra ever since the engine was replaced…
P0100 Mass or Volume Air Flow Circuit Malfunction
P0101 Mass or Volume Air Flow Circuit Range/Performance Problem
P0102 Mass or Volume Air Flow Circuit Low Input
P0103 Mass or Volume Air Flow Circuit High Input
P0104 Mass or Volume Air Flow Circuit Intermittent
Those are generic OBD II codes. There may also by Hyundai specific ones.
Note that every one of them refers to the circuit, not to the MAF itself. Without knowing the code or the diagnostic procedures used by the 2 places you’ve been to its hard to say anything specific.
Though do ask about the TSB as CSA noted below.
You’re not running a special aftermarket air filter such as a K&N are you? How is your air filter & its housing?
Probably not your problem, but I have a 2004 Hyunday Sonata and I got a CEL error code indicating MAF related faults. As I went in to clean the MAF, I saw a critter (mouse or chipmunk) had crawled into the air filter housing and chewed up the air filter into shreds (probably for bedding). All those shreds plugged up the intake screen - causing the CEL to illuminate.
I cleaned everything out, put a new air filter in, and the CEL turned off by itself in a few days. Then, a week later, the CEL came back on again. Sure enough, the new air filter was chewed to shreds!!! That’s when I got d-CON rodent bait, and it got rid of them for good.
You’re providing some good questions… not sure of any of the answers. We certainly fall in the category of know a little about the basics, but trust the mechanics when they say “use this part” or “replace that one”. Will ask these questions when I get the call today. Thank you for your thoughts.
possible… but we’ve had bait in our garage since spring. Will check though - would be nice if it’s that simple!
interesting that you mention the circuit … the radio seems to have an electrical issue - doesn’t work sometimes, have ruled-out the radio itself, seems to be in the wiring somehow. Also has often come back on or stopped working within a day of the work on the MAF. related?
code is coming in as P0172
Today’s code is P0172 (02 sensor, being replaced for $290)… is this logical?
as noted above - new code is P0172, does this make sense?
Peruse this: http://www.obd-codes.com/p0172
I think it is safe to say that the problem is something other than the MAF.
Diagnostics are tricky and time consuming and harder to make money on than just replacing parts. But maybe you need to find a shop that will spend the time on the diagnostics.
NO! Do not just let them replace the O2 sensor. There is some possibility that it may need to be done. But this is just shooting the messenger! Get you car out of that shop.
Update - Shop got the “ok” from husband to do the job before I caught up with him with your information. Still, I called the shop with reference to your questions and the information on the link you shared, and they became more interested in taking the car for a test, and checking other parts of the system. In the end, the technician chased us down as we were leaving to explain what he tried to do/what he found, and the shop had us leave without paying for a week to monitor how the car runs. Not likely we’ll return for future repairs. Thank you for your assistance.
Dunno if this is pertinent but my crown victoria has given me code P0171 a couple of times in the past 5 years (calls for lean bank 1 or 2 I forgot) auto places wanted to replace oxy sensor but I cleaned the MAF and that takes care of the problem, it is easy to clean with either tv tuner cleaner or now they sell a cleaner in auto supply.
So, it’s Saturday. We picked up the car Fri night, and the engine light is back on. We were sent home without paying for the repair for one week, the car lasted a day.