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Help with car issue! Is it transmission problem, or a bad sensor like MAF or TPS?

I have a 2000 Hyundai Sonata with 116k miles on it. In December, with 109k miles on it, I noticed after coming to a complete stop after highway or driving for a while that RPM's would drop to about .5 RPM and car would rumble and pull a little for a second and then go back to the normal .75 RPM idle speed. Brought car to transmission place in December thinking perhaps a bad torque converter, they replaced fluid and filter, (which was replaced at also 50k and 85k) cleaned wiring harness and told me they think transmission just getting old and needs rebuild. After I picked car up from garage in December, transmission was slipping going into 3rd gear, and rough/jerking shifts which I had felt b4 garage but not as bad or forceful.

Have been driving like this since December, and have found that I can avoid a slip into third gear by making a slight adjustment to how quickly I accelerate. Sometimes car drives great, sometimes its rough going into and out of gears. Check engine light has never illuminated, no codes and has never stalled when RPMs dip at stop.

Car always drove well in 4th gear, except for past two days when I felt a kind of hesitation while in fourth gear that comes and goes quickly. After I stopped at a light, the RPM revved above 1 and was making a noise as if I were putting my foot on the gas in neutral. When light turned green, I tried to accelerate and it was hesitated and almost felt like a misfire but not. This all has never happened. I tried to drive home, and had to stop at another light where it did the same thing - revved about 1.5 RPM and felt like it was trying to accelerate by itself. The car jerked with my foot on the brakes. Finally got home, sat in driveway at idle, and was completely fine in normal idle speed. Please, if you have any ideas, please help! I've just about had it with this problem, and I'd really hate to bring it back to a transmission place and have them tell me it needs a rebuild when it may be something like the Mass air flow sensor or throttle position sensor.

Update:

forgot to mention that when I start car up from cold, it revs around 1.5 RPM and can take up to 5 minutes to go to normal idle RPM level. Also, when I put car in drive from park, it goes almost immediately and I can't pick up any hesitation.

Update 2:

also when ac is put on, car jerks and has like no power... when i tried to put ac on the other day on highway, it felt like it was hesitating again in fourth gear. don't know if this helps

4 Answers

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  • 1 decade ago
    Favorite Answer

    1) Not Mass Air Flow sensor problem because MAF simply pre-heats the air that gets into the engine combustion chamber for better combustion.

    1a) But MAF could also be another problem area as manifested by your cold start problem; have this checked as well when you finally have the car tuned up as suggested below.

    1b) Throttle Position Sensor, or TPS is supposed to be reset only by a shop with diagnostic tool, and therefore not likely the problem unless tampered with.

    1c) No-fault lights at all when there should be one may mean a busted light or disconnected wire.

    1d) Check your fuel filter as well; frequent change because of dirt accumulation indicate that you should bring down your fuel tank for thorough cleaning.

    2) YES, most likely a transmission problem. This is only about an hour's job where the torque converter is replaced. Go easy on the accelerator as the problem may have been caused by your driving style. There are 'matic cars that go far beyond your driven distance and still in good driving condition.

    3) IF, despite the transmission solution, you still encounter the hi/lo RPM problem, change the engine harness (connecting the EFIs to the servo). This is a little hard to find (and if you find one, gets too expensive), go check the "junked cars park" and get one, spray the male/female terminals with "contact cleaner" (NOT with wd40) and connect. Then go to a shop with diagnostic tool and get a tune-up job (this includes resetting the TPS to factory specs).

    Driving a car with 'matic transmission should be like playing the grand piano.. Meanwhile, set to Neutral at red light.

    Source(s): I was into the automotive shop business before, now a supplier of automotive/vocational supplies and equipment.
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  • 4 years ago

    A bad MAF sensor will ALWAYS show up in an OBDII scan. MAny auto parts stores check you computer for FREE, at least in the USA. I do NOT believe that your MAF is bad. I DO believe that your IAC valve is dirty, and so is your throttle body. Take a few British pounds to the local oil change centre, and have them clean your T body and IAC valve to SHOWROOM clean conditions. The IDLE AIR CONTROL valve is absolutelyl CRUCIAL to proper fuel mixture. It fine tunes the amount of air entering your engine from signals made by your O2 sensors. It would be a BIG help if yo included the TYPE of car your have, Year, Make, Model, and Country of origin, even engine SIZE!!! NEVER buy sensor needlessly without a proper test. You will just waste money, and the REAL problem goes undetected!!! SInce you already diconncected your MAF, you will have to reset your engine computer because it will "THINK" that your MAF is bad. SO reset the computer, clean out your IAC and T body, and see what happens. Whatever your car is, it will profit by installing the newer Iridium type spark plugs. Fuel will chemically react with these newer plugs, More power, economy and lower emissions result. Expect up to 20% improvement by doin so. But make SURE your IAC is showroom clean FIRST OFF!! >>>>ALSO>>>> change your fuel FILTER. By changing your air filter, you have changed the air/fuel mixture. It is OBVIOUS that your iac IS VERY DIRTY. good luck!!

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  • demers
    Lv 4
    4 years ago

    It Transmission

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  • 1 decade ago

    Get rid of it and take the loss. You will lose all kinds of money trying to fix it.

    Source(s): Age and wisdom
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