Manifold Absolute Pressure sensor on the firewall. Failure causes rough idle, poor MPG, P0107/P0108. Five-minute replacement.
The MAP sensor measures intake manifold vacuum to inform the ECU about engine load. On 4.0L XJ it is mounted on the firewall (Renix and early HO) or on the throttle body itself (later HO). A small hose runs from the manifold to the sensor on firewall-mount versions; check that hose for cracks - a leaky MAP hose mimics MAP sensor failure. Symptoms: rough idle, surging, poor fuel economy, hesitation, codes P0106-P0109. Mopar 56029405 fits 1991-2001. Two screws hold it; one electrical connector. Five-minute job. Beware that K&N over-oiled air filters can contaminate the MAP sensor diaphragm and cause identical symptoms - if you run K&N and see MAP codes, clean or replace the sensor and reapply less oil.
| Part | Vendor | Est. price |
|---|---|---|
| MAP sensor Mopar | Mopar/RockAuto | ~$45 |
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.