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Jerry, Master Mechanic
Category: Hyundai
Satisfied Customers: 17217
Experience:  30 year ASE Master tech
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I replaced the battery in my XG300 and now my car wont idle.

Resolved Question:

I replaced the battery in my XG300 and now my car won't idle.
Submitted: 5 years ago.
Category: Hyundai
Expert:  Jerry replied 5 years ago.

Hello and welcome to Just, Super mechanic here. Please DON’T hit accept until you are completely satisfied with the answer. About your vehicle.

2001 Hyundai XG 300 V6-3.0L

The adaptive presets have to be relearned. That can be done with a scan tool, (that the dealership uses) or by normal driving. That happens a lot with them if the battery is disconnected. You can try going through a drive cycle and then it should idle normally.


Drive Schedule Notes:

  1. Coolant needs to be within 0 to 40 C (0 to 104 F) at start.
  2. Fuel level must be above 15% .
  3. When decelerating from 50-55mph there needs to be at least 5 seconds of fuel cut-off; its best to close throttle as soon as possible for 5 seconds to assure decel fuel cutoff occurs.
  4. Try to maintain constant throttle as much as possible during the steady state speed portions of the drive cycle.

Cautions :

  1. This schedule is best driven on a dyno if available, otherwise find the best road with least traffic
  2. Obey speed limits and drive safely.
  3. If you lose the schedule due to traffic, attempt to get back to it when conditions are safe to do so.
  4. Keep your eye on the road and avoid looking at the schedule constantly; its best to have a passenger describe the schedule to you while driving.

Customer: replied 5 years ago.
I have driven the car several times since the battery was changed and it still isn't idling. I have to press the accelerator and the brake at the same time when I sit in traffic
Expert:  Jerry replied 5 years ago.
Oh, I see. The first thing that I would do is clean the throttle body, (just to be sure it's not gummed up) and the IAC may not be moving to compensate for the engine loads to keep it idling. Of course you want be sure there are no vacuum leaks as well and the air intake hose is not leaking and it's on tight.

The idle speed is kept at the optimum speed by controlling the amount of air that bypasses the throttle valve in accordance with changes in idling conditions and engine load during idling. The PCM drives the idle speed control (ISC) motor to keep the engine running at the pre-set idle target speed in accordance with the engine coolant temperature and air conditioning load. In addition, when the air conditioning switch is turned off and on while the engine is idling, the ISC motor operates to adjust the throttle valve bypass air amount in accordance with the engine load conditions in order to avoid fluctuations in the engine speed.

Service and Repair


NOTE: Disconnect the intake air hose from the throttle body, and check the throttle valve surface for dirt. Spray cleaning solvent on the lace of the valve to remove dirt.

  1. Warm up the engine, then stop it.
  2. Remove the intake air hose from the throttle body.
  3. Plug the bypass passage inlet of the throttle body.
NOTE: Make sure the solvent does not enter the by-pass passage.
  1. Spray cleaning solvent into the valve through the throttle body intake port and let it soak for about 5 minutes . After 5 minutes open the valve and wipe it clean with a soft rag.
CAUTION: Keep the throttle valve closed while spraying to avoid charging the intake path with solvent.
  1. Start the engine, race it several times and allow the engine to run near idle for 1 minute .
  2. Repeat Steps 4 and 5.
  3. Unplug the bypass passage inlet.
  4. Attach the intake air hose.

  1. Disconnect the battery ground cable for more than 10 seconds .

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