Hey I have a 99 sonata. It's been giving me hesitation problems for quite a while. I had the code checked and it said "lean bank" p0171 (i think). We (a friend and I) checked to make sure that there was no vacuum leaks, we checked the fuel injectors, I replaced the spark plugs, and ran fuel injector cleaner. My friend was convinced that it was the MAF so he decided to unplug the MAF. It ran like a champ without any problems (no hesitation and no rough idle).

So i bought and just put in a Remanufactured MAF. With the remanufactured MAF, there is no rough idle and the hesitation is not as bad as it originally was, however, it is still there. My friend was convinced it was still the MAF so we once again unplugged it and it ran like a champ once again (no problems except for a horrible rotten egg/sulfur smell). We put the MAF back in and instantly it hesitated.

What do you guys think could be wrong? I searched around and some people say that remanufactured MAF's will not work. Is this true? If so, why the hell not and there has to be a cheaper alternative than buying a MAF from a hyundai dealership for over 400 dollars.

 

Did you buy a "new" MAF or a junkyard MAF?

You might have an intake leak you can't see too well, like the intake gasket, or a cracked intake manifold.

 

As i said in my first thread, it was a remanufactured MAF (when they charge you a core price if you don't give in your old part).

If the cause was a leak, wouldn't the problem (hesitation and rough idle) have presented itself even when the MAF was disconnected? Furthermore, if it was a leak, the problem would occur at all times since it should be leaking the same amount given similar senarios (i.e. it should always bogg down when I floor it). However, this is not the case. Sometimes when I floor it, it behaves as it should, however, other times it hesitates. This isn't limited to me flooring it either, sometimes it will happen when I am just cruising along and I add a small amount of power to go from say 47mph to 50mph. Furthermore, if it was a leak, why would there be two different types of hesitations? With the first MAF, the hesitation was profound! With the MAF currently installed, it doesn't hesitate as much (although it seems to be getting worse).

When the MAF was there (old part and the remanufactured) there was a problem (hesitation and rough idle), when the MAF was not plugged in, there was no problem (besides a rotten egg smell <----does anyone know why this smell was there? is it too much fuel being pumped in?).

As for the vacuum leaks, we tested it by spraying almost everywhere under the hood. We found one hose that needed replacing (which we replaced then and there), but it was not the major cause of the problem.

Is there anyway to test the intake gasket or the intake manifold other than spraying them?

 

Rotten egg smell (or sulfur) means too much fuel and the catalytic converter is not hot enough to burn it off. You're right about the MAF and the vacuum leaks. Try testing the MAF for resistance.

You need to join the hmaservice.com website. In there is the procedure for doing diagnostic work on the MAF. I'd download it for you, but it doesn't cut and paste.

Also, did you do a fuel pressure check? Change the fuel filter? You might not have enough fuel pressure to spray properly.

There is a TSB which talks about problems with the V6 wiring harness on the MAF, and a kit to replace the wiring harness #00-01-005.

 

Hey, here are some updates.

I put in a MAF from a junk yard Sonata (it was hit bad in the back and the engine looked like it was in much better shape than mine and no way in hell was I going to spend $400 for a new MAF) for $50. The hesitation calmed down significantly when it was first installed. As time progressed it got worse. I also sent the car to Flemington Hyundai (in new jersey) for a complete diagnostic. They originally quoted me $99 for a complete diagnostic so I was like "hell yea!" However, they are extremely stupid, they want to argue semantics over words they do not know (i.e. "misunderstanding" and "complete diagnostic" <-ask for details and you shall receive ), and they wanted to charge me $303 after keeping the car for a week and not doing anything at all. It was a horrible experience and I advise you all to NEVER GO TO FLEMINGTON HYUNDAI.

Ever since the trip to flemington hyundai, the car has gotten worse and worse with every passing day. It hesitates under partial throttle, under full throttle, and under almost no throttle at all (not all the time though). Two days while driving I decided to put the car in neutral (while moving) and floor it to see what happens with the revs. It went to 3k and was hesitating (IN NEUTRAL), then sped up to 6k whereupon I released the gas. I've floored it while in neutral and parked, same thing. It gets to somewhere between 3k and 4k in the rev counter and hesitates for a while before jumping to 6k. Sometimes it hesitates at 2k, sometimes at 1k (all while in neutral). The car is somehow putting itself under load.

As a result of previous posts and suggestions, my friend and I pressure tested the car earlier today. First we did it with a hand pump and we heard a leak by the fuel injector. We went to Lowes (it was after 8 so all auto stores were closed) and got a new O-ring and the adapter for his compressed air unit. After putting in the O-ring, and pressure testing with his air compressor, there were no leaks at all. However, that didn't solve the problem. The car was still hesitating in neutral. We were leaning towards a clogged Catalytic converter but our previous history with the MAF made us a little skeptical. We decided that if there was a clog, the clog and hesitation would still be there if we unplug the MAF. So we unplugged the MAF and presto, no hesitation at all. We plugged the MAF back in, but took the MAF and the air intake out of the assembly (it was just held in the air). The car stalled so that means the MAF IS working. We put the MAF and the intake back in the assembly and disconnected the front O2 sensor - hesitation still there. Plugged in the front O2 sensor and took out the back O2 sensor - hesitation still there. We now think it is the ECU or the harness. We tried finding the ECU, but it wasn't by the front passenger side and it was getting late so we didn't look it up (anyone know where it is?).

What do you guys think? Are we right in assuming that if it was mechanical, the problem would still be there if the MAF was unplugged vs plugged? What other suggestions do you guys have? Let me know.

BTW, the car is not a V6 so it doesn't have the wiring harness problem. As for the fuel pressure, my friend and I both do not have the tools to do that as of yet. Where would I go to get the tools for that (please link to the tool or tell me the name of the tool)? If it doesn't have enough pressure to spray properly, why would it work properly when the MAF is not plugged in?

I tried using the hma website, it is confusing and is using adobe SVG which isn't supported by Vista nor adobe. Therefore, I can't see any of the graphics. I know it's a lot to ask, but if anyone can see the pages I need, can you copy/paste or printscreen/paste?

 

From OBD-codes.com:

"A code P0171 may mean that one or more of the following has happened:

* The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
* There could be a vacuum leak
downstream of the MAF sensor.

Possible Solutions

Possible solutions include:

* In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
* Inspect all vacuum and PCV hoses, replace if necessary
* Check for a dirty fuel filter and proper fuel pressure"


If you think you have a fuel pressure problem, one way to test it is to disconnect the fuel line, turn on the ignition and observe the spray. If it sprays like a garden hose, then it's probably ok. Dangerous to do, and not highly recommended, but passable for the meatball mechanic. You could always replace the fuel filter, as it's cheap anyways. And take out the fuel pump and make sure the mesh screen is clean.

The hmaservice.com site always has that SVG graphics error, and I've never been able to remove it. Just ignore it and you'll see the graphics anyway. You can try to go to Adobe and download the SVG graphic plugin.