The Jeep 4.0L inline-six is one of the most durable engines ever bolted into a Wrangler, Cherokee, or Grand Cherokee. But from the factory, it leaves real power on the table — and the single biggest bottleneck is the throttle body. If you own a 1991–2006 Jeep with the 4.0L, swapping the restrictive factory 56mm throttle body for a 62mm high-flow unit is one of the best bang-for-the-buck upgrades you can do in an afternoon. Here's a complete guide based on a real-world install on a Cherokee XJ.

Why the Factory Throttle Body Holds Your 4.0L Back

Stock 4.0L engines ship with a 56mm throttle body. That bore is sized for emissions compliance and drivability, not airflow. Above roughly 3,500 RPM — exactly where you need power for highway passing, towing, or a steep grade — the 56mm opening becomes a choke point that starves the engine of air.

The common DIY fix is to bore the stock throttle body out to 62mm. That typically runs $40–50 at a local machine shop, and you'll still need to buy new gaskets and seals on top. Once you add it all up, an aftermarket billet unit starts to look like the smarter move.

What's in the iFJF 1724 62mm Throttle Body Kit

The iFJF 1724 62mm Throttle Body arrives as a complete kit, not just a bare casting. Inside the box you'll find:

• The 62mm CNC-machined throttle body, wrapped in protective cellophane
• New throttle body gasket and MAP sensor gasket
• A new fuel line with inline fuel filter
• Butterfly clamp, zip ties, and mounting screws
• The T25 security-hex bit you'll need to transfer your sensors

That last one matters: the factory fasteners are tamper-proof, and the kit throws in the exact driver bit so you don't have to buy one.

Is It Really 62mm? (Spoiler: Yes)

One of the first things worth checking on any aftermarket throttle body is whether the bore is actually the size it claims to be. Using a micrometer, the iFJF unit measures a true 62mm on both the entry and exit side — a straight 62mm bore all the way through, not a fake number.

Here's why 62mm is the right size and not bigger: 62mm is the actual diameter of the intake manifold opening on these engines. Go larger and the throttle body has to taper back down to mate with the manifold, which cancels out the airflow gain. 62mm is the sweet spot where the bore matches the manifold perfectly.

Step-by-Step Installation (About 45 Minutes)

The install is a direct bolt-on with basic hand tools. No tuning required — the factory ECU adapts its fuel trims automatically.

1. Remove the Old Throttle Body

Disconnect the negative battery terminal first. Then unhook the intake tube, unplug the three electrical connectors (the IAC idle air control, TPS throttle position sensor, and MAP sensor), and remove the four 10mm bolts holding the throttle body to the manifold. The whole unit lifts right off.

2. Transfer Your Sensors

You'll reuse your existing IAC valve, TPS sensor, and MAP sensor — the new unit doesn't include them. Remove them from the old throttle body using the supplied T25 security-hex bit, then bolt them onto the new unit with the fresh gaskets. Pro tip: place the gasket on first, then start the screws, so you don't tear the new gasket while aligning the sensor.

3. Mount the New Throttle Body

Set a new gasket between the throttle body and the intake manifold, bolt it down in a cross pattern, and reconnect the intake tube, fuel line, and all three sensor connectors. One critical warning: don't drop anything into the open intake manifold — anything that falls in means pulling the cylinder head to fish it out before it damages a piston.

4. Start It Up and Idle

Reconnect the battery and fire it up. Let it idle for about five minutes so the ECU learns the new idle-air parameters. There should be no check engine light — the 62mm bore is well within the factory computer's adaptive fuel-trim range.

Real-World Results: Throttle Response and Smooth Idle

After the swap, the most immediate change is a noticeably smoother idle and sharper throttle response. On the test Jeep, the owner reported the 62mm throttle body delivered the single most noticeable change in throttle response and acceleration of any bolt-on mod so far — with "no hesitation" and no check engine light.

One thing to note: if you already run a throttle body spacer, the stock-length bolts that come with the kit may be too short, so you'll reuse your existing hardware. Without a spacer, the supplied bolts with the allen head make the install completely painless.

Another welcome detail: there's no core charge, so you keep your factory throttle body as a spare — or bore it out later if you ever want to experiment.

Does Pairing a Throttle Body Spacer Help?

Yes, and the two mods complement each other. A 62mm throttle body + throttle body spacer works on both ends of the intake equation: the spacer adds plenum volume and (in a helix/spiral design) creates controlled air turbulence for better air/fuel mixing, while the 62mm bore removes the downstream restriction. Together they're a logical pairing for a stock 4.0L that spends its life between 2,000 and 4,000 RPM.

Frequently Asked Questions

Will a 62mm throttle body cause a check engine light?

No. The 62mm bore is within the ECU's adaptive fuel-trim range. The factory computer automatically adjusts idle air control and fuel mapping — no CEL and no tune required.

Do I need a cold air intake to see gains?

You'll feel the improvement with the stock airbox. A cold air intake removes the upstream restriction while the 62mm throttle body removes the downstream restriction, so pairing them maximizes the benefit.

Is 62mm too big for a stock 4.0L?

No — 62mm is the sweet spot. It matches the intake manifold's actual opening, so you get maximum airflow without the part-throttle drivability issues that come with oversized bores.

Will this fit my 2.5L four-cylinder?

No. The 4.0L inline-six only. The 2.5L uses a different bolt pattern and would be over-bored at 62mm.

Can I leave my throttle body spacer on?

Yes, but you'll need to reuse your existing bolts since the kit's bolts are sized for a direct bolt-on without a spacer.

Shop the Full Upgrade

Ready to let your 4.0L breathe? Pick up the iFJF 1724 62mm Throttle Body and browse our full range of Jeep 4.0L performance parts to finish the job.

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