A full throttle body service on the 4.0L means cleaning the bore and butterfly, servicing the IAC, and confirming the throttle position sensor reads where it should. On Renix Jeeps (1987-1990) the TPS is adjustable and has to be set; on HO Jeeps (1991-2001) it isn't, so you verify it instead. This guide covers both.
Carbon builds on the back of the throttle plate and around the bore from PCV vapors, and over a few years that buildup narrows the idle bypass enough to make the engine hunt, stall at stops, or idle high. Cleaning the throttle body fixes that. But cleaning is only half the job — if the throttle position sensor is out of spec or has a dead spot, you get the same symptoms plus hesitation off idle, hard shifts on automatics, and sometimes a check engine light. The TPS tells the ECU exactly how far the throttle is open, and on the automatic-equipped Renix trucks it also feeds the transmission controller, so a sensor that's reading wrong can confuse both at once.
The single most important fact to get straight before you start: **the Renix TPS (1987-1990) is adjustable and the HO TPS (1991-2001) is not.** Renix sensors mount with slotted holes and have to be dialed in with a multimeter to a target voltage. HO sensors bolt on one way only and are either in spec or replaced — there's nothing to turn. Confirm which one you have before you order a part or reach for a Torx driver, because the procedures diverge completely at the sensor.
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| Part | Vendor | Est. price |
|---|---|---|
| CRC throttle body cleaner | Amazon / auto parts | ~$9 |
| Throttle body to intake manifold gasket (4.0L) | Mopar / Fel-Pro / RockAuto | ~$10 |
| Throttle Position Sensor (1991-2001 HO, non-adjustable) | Mopar / Standard Motor / RockAuto | ~$35 |
| Throttle Position Sensor (1987-1990 Renix, adjustable) | RockAuto / Crown Automotive | ~$45 |
| Idle Air Control (IAC) valve | Mopar / Standard Motor / RockAuto | ~$40 |
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.