2000 Hyundai Elantra transmission keeps shifting

Tiny
DARYLLOCKHART
  • MEMBER
  • 2000 HYUNDAI ELANTRA
  • 126,800 MILES
Where I live its hilly so I am constintly going anywhere from 50-60 mph so it keep it keep reving up when I take my foot off the gas pedal to coast and you can feel the car shift gears there isnt any warning lights on the tranny was low then I filled it and still does it even at 70-75mph but not as bad it seems if I keep my foot on the pedal ( under load ) it seems to take care of the problem
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Tuesday, September 3rd, 2013 AT 2:00 PM

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Tiny
CARADIODOC
  • EXPERT
Did you proofread that huge sentence with no punctuation?

"there isnt any warning lights on the tranny"

"the tranny was low then I filled it"

"it keep reving up when I take my foot off the gas pedal to coast"

"if I keep my foot on the pedal ( under load ) it seems to take care of the problem"

Does that mean the engine speed increases when you release the accelerator pedal, but it doesn't increase when you press the pedal?

You're doing yourself a disservice by not describing the problem coherently. You deserve a well-thought-out answer but no one will be able to figure out the symptoms. I'd repost this and include the engine size, exactly what is taking place, and any other observations. The best I can offer is to check for vacuum leaks when engine speed is too high, and to have the diagnostic fault codes read. Many auto parts stores will do that for you for free. Be aware that fault codes never say to replace parts or that they're bad. They only indicate the circuit or system that needs further diagnosis.

Don't reply back to this thread unless you think I can be of further help. Only you and I will get an e-mail notification that a reply has been posted. None of the other experts will see this or have a chance to help. There are some people here who are real familiar with your vehicle and may know exactly how to solve the problem.
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Tuesday, September 3rd, 2013 AT 8:29 PM
Tiny
DARYLLOCKHART
  • MEMBER
I own a 2000 Hyundai Elantra with a 2.0 and an automatic transmission. When I start my car it revs way up unless I tap the gas pedal. While driving the car jerks back and forth like its shifting constantly. There is not any trouble codes to read other than a red air bag light. The car even feels like its shifting when I am going down the highway at 70+ mph. It seems to drive better if I rest my foot on the gas pedal as to give it just enough gas to keep it under load, and not accelerate. I wiggled my MAF sensor and the car revs up slightly then back to normal idle. I am going to clean my MAF sensor and see if that has anything to do with it. I thought there maybe a problem with the transmission so I checked the fluid and it was very low, so I filled it to the correct amount, it didnt fix the problem any tho. I have been searching the internet for ideas and that is how I got the idea to check the MAF sensor.
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Wednesday, September 4th, 2013 AT 4:37 AM
Tiny
DARYLLOCKHART
  • MEMBER
Oh I forgot the gas mileage is terrible like I have put in $50 and have only driven 150 miles
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Wednesday, September 4th, 2013 AT 4:39 AM
Tiny
CARADIODOC
  • EXPERT
I'm not the driveability expert I wish I was but I can offer a few suggestions. Normally high idle speed is caused by a vacuum leak, but if it comes down when you tap the gas pedal you might want to look at the throttle position sensor. It actually doesn't have anything to do with idle speed but it tells the Engine Computer whether you're moving the throttle, which way, and how fast so the computer can anticipate the fuel needs of the engine without a hesitation when it waits to see the air flow change in the mass air flow sensor. It also tells the computer when you're at idle and when you're at wide-open-throttle. In general terms, that sensor is fed with 5.0 volts, and the signal voltage going back to the computer will always remain between 0.5 and 4.5 volts. When there is a hard defect in the sensor or its wiring the voltage will pop up to 5.0 volts or drop to 0.0 volts. THAT is what is needed to set a related diagnostic fault code. My reason for explaining that is that dirt inside the sensor, or a worn spot on the carbon element can cause an incorrect reading resulting in performance issues, but as long as that wrong reading stays within 0.5 and 4.5 volts, no fault code will be set.

Before you go through the work of cleaning the mass air flow sensor, you might try introducing a little extra fuel into a vacuum port. Propane is what is used most often. The Engine Computer calculates how much fuel to command from the injectors based on the weight of the air being measured by the mass air flow sensor. The sensing element is heated up which changes its resistance, then it gets cooled down by the air rushing past it. If the sensing element is dirty it will be partly insulated, won't cool down as much as it should, and the computer will interpret that as less air flow. You'll have to push harder on the gas pedal to get the right amount of fuel but that opens the throttle blade more so more air comes in, ... Just like when there's a vacuum leak.

Even at idle, the computer is in control of idle speed and it may be targeting what it knows as the correct amount of fuel, and the extra air causes the engine speed to increase. As with the throttle position sensor, tapping the gas pedal will increase air flow and that may affect the element in the mass air flow sensor.

You or your mechanic may also get an idea of what is happening by watching live data on a scanner. For this I have to defer to my Chrysler experience. They use a "stepper" motor to screw a pintle valve in and out of an air passage around the throttle blade. That valve has 256 possible settings called "steps", (not related to stepper motor). At step 0 the valve is fully closed. Step 32 is about typical for a properly-running engine. With one cylinder misfiring you'll find it at about step 50. When there is an idle speed problem, you can look at the step the motor is being commanded to to get an idea of what is happening. If idle speed is too high and the motor is at a low step number or at "0", the computer is trying to reduce idle speed but not having success. That's where you'd be looking for a vacuum leak. If the step is high, typically much higher than about step 32, the computer is attempting to raise idle speed in response to something. It may do that when the AC compressor kicks in, or when the steering is turned which puts an additional load on the engine. The power steering pressure switch, (when used), will be listed on the scanner as "on" or "off", or "low" or "high". Those things should match what is taking place on the car. For example, the power steering switch should read "high" when you're turning the steering wheel. If it reads "high" all the time, the computer thinks there's a load on the engine when there isn't, and it's bumping up idle speed to handle that load.

Other manufacturers use "percent" of full-open idle air valve instead of "steps". There's two different designs of this valve for your car. One uses the stepper motor, similar to Chrysler and GM, and one looks like a spring-loaded solenoid similar to what Ford uses. This valve design has two hoses attached to it. I would look at those hoses for signs of dry-rotting, cracking, or loose clamps. This valve, in any application on any car brand, is a controlled vacuum leak. Any air that sneaks in through an uncontrolled vacuum leak will raise idle speed.

If you can keep the engine idling too high you can try blocking various vacuum hoses to see if one brings the speed down. If one does, follow it to its branches and do that on each one to narrow down the source of the leak. There could also be an emissions system valve that is turning on to purge the charcoal canister of its stored fuel vapors. They typically aren't supposed to open at idle but a valve could be stuck, or the computer might be commanding it open because it thinks the engine is not at idle speed.
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Wednesday, September 4th, 2013 AT 2:08 PM
Tiny
DARYLLOCKHART
  • MEMBER
Earlier I said I did some research on my symptoms, bfore I went to town about 20 miles I had seen that try tapping on the MAF sensor or the TPS. Well it worked for the 20 miles, on my home the rpms were jumping again but not as bad. I did however pull the MAF sensor out and sprayed it with the recommended spray. Earlier I had said I wiggled both the TPS and MAF sensor, it was the TPS that made the car rev a little I wonder if there maybe a loose connection, but the pigtail is like $ 38 from adavanced auto and the TPS is $55 so I'm not sure which one to buy first. NOw that you said some thing about the purge cannister I remember years the car was having troubles with that. Oh and another thing when I pulled the hose for the MAF senor there was oil or something tha looked felt and smelled like oil in the hose, also some in the throttle body, not a ton but enough to drip off my finger
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Wednesday, September 4th, 2013 AT 4:09 PM
Tiny
DARYLLOCKHART
  • MEMBER
Thanks for your help and responding I will let you know what happens when I change TPS but it wont be till friday so thanks again
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Wednesday, September 4th, 2013 AT 4:11 PM
Tiny
CARADIODOC
  • EXPERT
You really shouldn't be able to change anything by wiggling if the problem is inside the TPS because that's pretty well sealed. The terminals in the connector are the first suspect. Look for signs of corrosion or dullness on the terminals. You may be able to sneak a little piece of sandpaper inside the TPS connector to shine up the terminals. Try to use a pick to squeeze the terminals tighter in the connector body. You can also pull each terminal out, one at a time, and squeeze them tighter. There's usually a locking wedge to pry out, then plastic fingers to move to release each terminal.

Sometimes just unplugging the connector repeatedly will shine the terminals up from the scratching action. That is never a permanent fix but if it solves the problem for a day or a week, you know where the problem lies.
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Wednesday, September 4th, 2013 AT 4:23 PM
Tiny
DARYLLOCKHART
  • MEMBER
I think I am going to put a new pig tail on it then I know it will be a good connection and then I will shine the terminals as you said. Is there any reason there would be oil in the air hose. The air filter isnt very dirty but I will replace anyways. Thank you I do believe the problem lies in the connection or the TPS itself so I have it narrowed down.
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Wednesday, September 4th, 2013 AT 6:47 PM
Tiny
CARADIODOC
  • EXPERT
Oil in such places is usually from condensed vapors. Sometimes replacing the PCV valve will solve that.
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Wednesday, September 4th, 2013 AT 9:00 PM

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