Car running rough after it sits over night

SOURCE: '01 Elantra Start-up issue

i think you should change the fuelfilter.

SOURCE: 2004 Hyndai Elantra starts, runs for 1-2 sec. then shuts off.

Your car may have an "immobilizer" which is part of the security system. It will start and stall if someone uses an "unauthorized" key to start it. In other words, a key that was not programmed by Hyundai or the dealer to run the engine. This happens if you had repairs done and immobilizer was interrupted and all keys were not present for programming and you're using one of those keys perhaps and sometimes it just loses its frequency. These systems often have a different frequency each time they're coded so all keys must be programmed at the same time every time. Sometimes the immobilizer coding process is simple and included in the owners manual...NOTE: this could be an indication of a bigger problem if it keeps happening.
Good luck

SOURCE: 05 Santa fe 3000 rpm vehicle stops, turn off wait restart runs like new

seems like engine goes to "save run" mode. the reason why is stored in the onboad computer usualy. have someone read that error code with an OBD interface, and act accoringly to that code.

SOURCE: Engine idling high in park. Will not start until

check your IDLER

PAUL MC G

• 1280 Answers
• Posted on Oct 19, 2009

SOURCE: hesitation when accelerating. when tac is over 2K

Sounds like misfire... Did the 'Check Engine' Light come ON? Whenever the 'CHECK ENGINE' light comes on, the ECU (Engine Control Unit) sets a Diagnostic Trouble Code (DTC). These codes identify the particular engine management system which caused the light to come on.
You'll need to use/find an OBDII (On-Board Diagnostic) Scanner to retrieve any code which have been stored in the ECU computer. Afterward, we might be able to help you DIAGNOSE and perhaps eventually fix the problem.