Intake Manifold Gasket Replacement — 4.0L XJ

Difficulty: intermediate

A leaking intake manifold gasket on the 4.0L shows up as a rough idle, a lean code, and an engine that won't settle down — this guide covers replacing the intake/exhaust combination gasket on 1987–2001 XJs.

If your XJ idles rough, surges, throws a lean code (P0171 on OBD-II trucks), or makes a hissing sound that changes with throttle, a failed intake manifold gasket is a strong suspect. On the 4.0L the intake and exhaust manifolds share the same studs on the side of the head and seal against one combination gasket, so the two jobs are linked — which is why most people do this gasket at the same time they chase a cracked exhaust manifold (the XJ's other famous leak in this area). A leaking intake gasket pulls unmetered air into the engine, leans out the mixture, and makes the truck run poorly cold and hot. Ignore it long enough and you'll be cleaning up burned valves and a confused fuel trim.

Before you tear into it, confirm the leak. Spray a little brake cleaner or carb cleaner along the intake-to-head seam with the engine idling — if the idle changes, you've found unmetered air getting in there. That five-minute test saves you from pulling a manifold that wasn't the problem.

This is an intermediate job, not because any one step is hard, but because there's a lot crossing the manifolds and the fasteners have been heat-cycled for decades. Budget time for stuck studs, plan to replace the exhaust manifold if it's cracked while you're in there, and respect the torque spec — the front and rear studs snap if you lean on them.

Why it works

Fixes the root cause of a rough idle, surging, and lean codes instead of masking it.
Done alongside an exhaust manifold replacement, you handle both of the XJ's classic side-of-head leaks in one teardown.
Gasket cost is modest ($40–120 with hardware); the value is in the labor you keep.

Trade-offs

Seized and broken exhaust studs are the real risk — a snapped stud in the head can add hours and an extraction.
A lot of components cross the manifolds, so reassembly demands care to avoid pinched harnesses or missed vacuum lines.
The dual-purpose OEM washers/clamps are easy to lose track of and can't be substituted — keep them organized or the manifolds won't seal.

Tools required

Metric socket set with extensions and a swivel/U-joint
Torque wrench (ft-lb range)
11mm and 13mm sockets (manifold fasteners)
Gasket scraper or plastic razor
Penetrating oil
Brake cleaner and shop rags
Flare-nut wrenches (fuel line, if disconnecting the rail)

Parts

Some parts links are Amazon affiliate links — if you buy through them Trail Manual may earn a small commission at no extra cost to you. We only list parts we’d run on our own rig, and never on safety-critical pages.

Part	Vendor	Est. price
Intake/exhaust combination manifold gasket — Fel-Pro MS93094 (1999–2001 HO)	RockAuto / Summit Racing / O'Reilly	—
Intake/exhaust manifold gasket — Fel-Pro MS90949 (1987–1995 RENIX and early HO)	RockAuto / Summit Racing	—
Manifold-to-head dual-purpose washers/clamps (OEM design)	Mopar / RockAuto	—

Sources

{'title': 'Jeep Cherokee Engines — Intake / Exhaust Manifold Torque Specs (lunghd.com)', 'url': 'https://www.lunghd.com/Tech_Articles/Engine/Manifold_Torque_Specs.htm'}
{'title': 'Intake/Exhaust Manifold Tightening Sequence — NAXJA Forums', 'url': 'https://naxja.org/threads/intake-exhaust-manifold-tightening-sequence.1115555/'}
{'title': '1999 Jeep 4.0L Fastener Torque Specs (Scribd)', 'url': 'https://www.scribd.com/doc/306417247/JEEP-4-0L-Fastener-Torque-Specs'}
{'title': 'FEL-PRO MS 93094 Intake and Exhaust Manifolds Combination Gasket — manufacturer listing', 'url': 'https://www.jegs.com/i/Fel-Pro/375/MS93094/10002/-1'}

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.