I have a 2001 hyundia elantra problem i am having is weather it has just been started or is up to operating temp. it will rev to almost 3k then down to 1500then back up to 3k then back down i believ this would continue all day long anyhow i thought it would be a bad idle control sensor so i replaced it and still problem exist i checked vacum lines for leaks but did not find any

Hi,
The problem is in either the idle speed actuator or the TPS - throttle position sensor.
Have both these checked, the accelerator is electronic and it keeps on thinking that the throttle is down but tries to switch back to idle. Get these checked and let me know if you need more information.
Thanks
Jason

Hi.

The misfire (eg. P030X) is consequence of the real fault. If the other code is idle air control sensor, and the sensor has already been replaced, then it is either wiring to sensor or IAC valve stuck.

Here testing procedure:

Disconnect the idle speed control valve wire and check if the idle rpm goes down.

Remove cruise control cable and throttle cable. Check if the idle rpm speed goes down.

With ignition switch in on position, test the idle speed controller. Ground the Gray wire and check if you hear a click. Ground the Green wire and see if idle speed controller is clicking. With the vehicle running, ground each winding and see if that makes a difference in the idle speed.

Test for vacuum leaks. Remove the cap on throttle body. With the engine running, block both ports in front of the throttle body and see if the idle speed drops. The engine should stall with both ports closed.

If the other code is a P0507, that is Idle air control RPM higher than normal, rather than p0500 or p0501 (IAC sensor) in that case also have a look at MAF sensor.

Resuming

If code is Idle air control sensor (P0500/P0501), then check wiring to IAC control . This is done following procedure above.

Clean IAC valve valve.See: How to Check an Idle Air Control.

Symptoms can also be caused by or vacuum problems.

About vacuum, small leaks are difficult to spot, often there is no hissing noise. A good way to do the vacuum testing is by placing a gauge like this in vacuum lines:

With the gauge in place, spray carb cleaner on the hoses. If there is a leak, carb cleaner will temporary close the leak, and pressure will go up a bit, as vacuum will stop aspiring air through the leak.

I dont think problem is vacuum leak, sensor is also unusual. Check IAC valve and system.

If you repute my solution helpful, then please take some times to accept the solution. Providing good repair tips requires time and skills, and your feedback is important for us.

Regards.

Ginko.

Hi! The problem will be on the MAF (mass air flow) sensor. The MAF has big contribution on engine performance specially on the idle and vacuum supply. If the MAF is faulty you'll have an unusual idle. Have it replaced and you'll be good. Hope this helps and thank you for using FixYa!

Try changing the fuel filter. You may be experiencing vapor lock symptoms. Good luck!

It could be several things causing this. Is your check engine light on? If so go to Autozone and have them put it on their diagnostic computer and check codes. This is free and will give you an idea where to start looking. It could be the Mass Air Flow sensor, the ECM trying to lean the motor out, it could be a dirty air filter, could be several things.

If this is something that occured all of the sudden, unplug the vacuum hose from the vacuum booster behind the brake master cylinder. Plug the hose and see if the idle settles down. If it does, replace the brake booster. Let me know, also, what codes have been pulled?