Carbon buildup on the throttle plate causes high or hunting idle. CRC throttle body cleaner, soft rag, do not scrub the IAC pintle bore.
Idle quality on the 4.0L is closely tied to a clean throttle body. Over time the back of the throttle plate and the surrounding bore accumulate oily black carbon from PCV vapors, narrowing the bypass airflow and causing the Idle Air Control valve to hunt or stall. Remove the air intake tube from the throttle body, hold the throttle open by hand, and spray CRC Throttle Body Cleaner (not regular carb cleaner - the propellants attack the TPS) onto the plate and bore. Wipe with a clean lint-free rag. Do NOT scrub or spray cleaner into the small cylindrical bore where the IAC pintle sits - the IAC is closely toleranced and aggressive cleaning will damage the pintle tip. Reassemble, start, and the ECU will relearn idle in a few minutes. A drive cycle locks in the adaptive learning.
| Part | Vendor | Est. price |
|---|---|---|
| CRC Throttle Body Cleaner | auto parts | ~$9 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.