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Discussion Starter #1
My 2001 optima 2.4 4speed automatic has 138,000 miles on it.

lately, there is poor and jerky hesitation when it is first started.

I pulled the intake manifold, cleaned the throttle body and manifold.

But this did not get rid of the problem. After that, the p0171 code showed up indicating a lean fuel/air mix.

I did some research on the internet and found out that people have been cleaning the Manifold Air Flow Sensor on various fuel injected cars for better performance.

So I followed the best instructions I could find:

The MAFS is located in the rubber intake tube between the air filter and the throttle body. I removed the MAFS and the tube housing it is mounted on. The honey comb screen/grilled was dirty too the touch, kind of sooty.

then removed the MAFS from the tube by dremel cutting the torx 'non-tamper' screws so that a flat head could work.

I pulled the MAFS out of the tube (it is sealed by an O-ring, no gasket) and sure enough, on the metallic wires, there was sooty dirt.

Apparently the MAFS measures airflow by how fast it cools off: the little electrodes are heated to a certain temperture--when air flows through it, they cool off. More air means more cooling, this data tells the ECU how much air is flowing. So it makes sensed that if the electrodes are covered in dirt/soot, this would impact the operation.

I cleaned the part by blasting it with CDC QD electronic parts cleaner, available at autozone, etc.

Don't use carb cleaner, soap, etc, and don't physically touch the metal sensors.

This cleaned it right up, and now the car doesn't hesitate or jerk around in the morning when it is getting up.

Still too early to tell about the p0171 code--Ihave reset that code before only for it to come after about 30 miles. But it makes sense: a dirty MAFS would be an insulated MAFS. Logically, this would mean more air would need to flow to cool it than if it were clean. So more air would actually be flowing that the ECU thinks is flowing, because the MAFS is underreporting the amount of air due to the insulation.

More air would indicate a lean air fuel ratio, which is consistent with p0171
 

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2002 Kia Magentis 2,0 LPG
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Thanx ekubec....
This is a very usefull instruction...
I'm thinking of cleaning my intake manifold also... because my my idle is a little irregular,probably because the idle speed control actuator is dirty....
How hard is it to dissasemble the manifold and do you have some pictures, that would be great....
Thax
 

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Discussion Starter #4
Dissassembling the manifold was quite easy. There are lots of bolts, but very easy to get to.

Sorry, no pictures. Keep meaning to take some when I do projects.

In retrospect, pulling the manifold off of the head was probably unnecessary.

The throttle body was dirt and needed cleaning, and this can be pulled off of the manifold. Use carburetor cleaner. The service manual says to be careful not to get cleaner in the idle bypass chamber or something--there are a couple of passages there and it recommends plugging them, although I did not.

I would pull the throttle body and the MAFS, clean those both and see if you get better results. leave the manifold on the engine
 

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2002 Kia Magentis 2,0 LPG
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Thanx, i'll get on it as soon as finish with my exams...
let you know how it goes...

Thanx again...
 

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2001 Kia Optima
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Did the check engine light remain off after this as well?

Thanks for the instructions. I will try this as well.
 

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Please help me... my kia sorento 2011 4 piston have a hicugh during acceleration with hesitation espetially when the car is hot..when the car is cold it run smoothly.i changed air filter feuel filter and sparkplug also i cleaned throttle body but no benifit then i checked it by computer no error...what shall i do?? Pleade your help
 
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