Question about 2001 Hyundai Sonata

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01 hyundai sonata running rough-cont

I think i figured out (or i hope-havnt got it yet) what the problem is-the mass air flow sensor-the rpm's doesnt go up like they are supose to when you disconnect it-thanks again for your help-by the way, youre hot and no, im not a guy, adrienne

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  • csbanks22 Mar 20, 2009

    I have a 1999 Sonata, 5sp, and it is losing power. I have replaced the pcv valve, O2 sensors, etc. I have been told that the mass air flow sensor may need to be cleaned, but I don't know where it is located.



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The mass airflow sensor can definitely cause the problem, but I'm not sure that it's the problem in your case. If you disconnect it, the car's computer doesn't know what amount of air is coming into the engine, so it switches to some default operating parameters that are programmed into the computer. Many times it'll do as you said - it'll limit the RPM for one thing, and for another it'll richen up the fuel delivery (you may see black smoke out the back of the car when you rev it - that's excess unburned fuel, which the engine adds to keep it from being damaged). If you plug in the mass air sensor again and the engine's operation returns to "normal", then you should try getting some Air Intake and Throttle Body Cleaner from any local parts store, spray it into the intake piping, and allow it to dry. You don't want to scrub the sensor element because it could be damaged. You could spray it in with the engine running, which will help additionally because the cleaner will also help to de-carbon the throttle body and backside of the valves as it goes in. It's meant to be burned in the engine, so it won't hurt anything - just make sure that you spray quick bursts and not a long, soaking stream - that can foul the mass air sensor.

Another possibility is that your primary oxygen sensor (the one before the catalytic converter) is starting to go bad. Have you noticed diminished gas mileage at all? That's an indicator as well of either mass air sensor or oxygen sensors. As a long shot, you may have a problem with the coolant temp sensor - if it's reading poorly, it could be telling the computer to fuel the car incorrectly and causing the bucking that you have seen.

I'm not able to see your original posts here (I'm on a friend's computer about two hours from home), but I have them bookmarked at home and will go back through them when I get home tonight. So forgive me if I duplicate some information or ask about something you posted. Have you verified that the plugs and spark wires are up to par? If they're corroded or worn, they could cause rough ignition and make the car shake and stutter.

A final idea of what to look into would be the fuel filter - does the car buck and kick at idle, or when you're on the road driving and give it gas? If the fuel filter is clogged, it'll have trouble supplying the extra fuel needed when you hit the gas to merge into traffic or pass someone.

If it's easier for you, email me at and I'll be able to walk you through these ideas more efficiently, as I check the email pretty often:)

Posted on Jan 01, 2009


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