Got a 2000 with 120k on it. I've got a little stutter under load. No SES and it idles fine. Just seems like it's struggling sometimes at hwy speeds. Finding myself having to depress the gas enough to downshift on long hills.

 

Unless you have any check engine light (pull codes for your roadmap) it is time for some testing.

1. Verify fuel pressure. For a 2000, you should have 49 psi, plus or minus 5 psi. Must be done with a gauge; no shortcuts. Many parts stores will rent you this gauge very inexpensively if you don't have one. The job takes 15 minutes.

2. Test throttle position sensor. More on that below.

3. Be sure plugs are fresh. Not likely your issue; just good maintenance. I like NGK copper plugs for your vintage. Gap is .035
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The throttle position sensor is connected to the throttle shaft on the throttle body. It sends throttle valve angle information to the PCM. The PCM uses this information to determine how much fuel the engine needs. The TPS is really just a simple potentiometer with one end connected to 5 volts from the PCM and the other to ground. A third wire is connected to the PCM. As you move the accelerator pedal with your foot, the output of the TPS changes. At a closed throttle position, the output of the TPS is low, about a half a volt. As the throttle valve opens, the output increases so that, at wide open throttle, the output voltage should be above 3.9 volts. Testing can be performed with an electrical meter. Analog meter is best. You are looking for a smooth sweep of voltage throughout the entire throttle band. While slowly opening and closing the throttle, take note to the movement of the voltmeter needle. There should be a direct relationship between the needle motion to the motion of the throttle. If at anytime the needle moves abruptly or inconsistently with the movement of the throttle, the TPS is bad

You should have 5 volts going into the TPS. At idle, TPS output voltage must be greater than 200 millivolts. At wide open throttle (WOT), TPS output voltage must be less than 4.8 volts.. The best is to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts. One of the other wires should show .26V (or so). The other wire will be the ground and should show no voltage. Move the throttle and look for smooth meter response up to the 4.49 at WOT.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.

The TPS is sensitive to heat, moisture and vibration leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced. A TPS may fail gradually leading to a number of symptoms which can include one or more of the following: -

NOTE: The throttle position sensor is also DIRECTLY involved with transmission shifting characteristics! It should be verified early in the troubleshooting process, when a transmission issue is suspected!

• Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".
• High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction with a slow engine return to idle speed symptom.
• Slow engine return to idle: A failing TPS can report the minimum throttle position values incorrectly which can stop the engine entering idle mode when the throttle is closed. Normally when the throttle is closed the engine fuel injectors will be deactivated until a defined engine RPM speed is reached and the engine brought smoothly to idle speed. When failing a TPS will not report the throttle closed and fueling will continue causing the engine to return to idle very slowly.
• Engine Hesitation on Throttle Application: The TPS is also used by the ECU to determine if the driver has applied the throttle quicker than the Manifold Air Pressure sensor can read. The fueling is adjusted accordingly to cope with the sudden increase in air volume, however a faulty sensor can cause the ECU to ignore this data and the engine will "hesitate" when applying the throttle. In extreme cases with the engine at idle, a sudden application of full throttle can stall the engine.
• Engine Misfire: A fault TPS can report values outside the denied acceptable range causing the ECU to incorrectly fuel the engine. This is noticeable as a slight misfire and can trigger the misfire detection software and/or Malfunction Indicator Lamp (MIL) light on the dashboard. Extreme cases can cause excessing misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.

 

I just replaced my coil pack and spark plugs and tps. Running alot better. I would say over 100k than there likely at risk of failure. Its always annoying to replace that dumb thing. Especially on mine because i have custom brackets bc i have an older style cylinder head.

 

Excellent info. Plugs are new. (replaced the head about 3,000 miles ago) I'll go ahead and replace the TPS since it is cheaper than coil packs and test my fuel pressure.

 

The coil rails on the 00-01 XJs are quite robust and rarely fail. I would rule everything else out before condemning the coil rail unless there is an obvious external crack or physical damage.

 

My OE coil pack died at about 150K .

 

151k on my coil packs, and they work fine. I'd suspect a dozen other items before looking at the coil packs --they're quite reliable. I agree with TJWalker - it's time for some testing to determine the cause of your problem, rather than demonizing coil packs.

 

Of course your mileage may vary but we have 2000's with 300k and one with 260k and both packs are stock. Our stutters were the cam position sensor there by the oil filter.

 

Coil packs would throw a code. I have 50 cents that says fuel pump.

 

I have 50 cents that says 6 year old thread.

 

LMAO ayup sure nuf

 

I have 50 cents that says people still drive these and this thread was found in a 'search'.
Not much worse than not searching, then posting a duplicate thread and getting drilled for it. Cannot please everyone.

 

No, but everyone can pay attention to the date of a post.

 

Why should I not post to one that is open no matter the age? I did note the date. Seemed like an ongoing thing.
If it was that taboo I would think it would have been closed by an admin of moderator. Been at this for about 50 years and I will still be wrenching.

 

They are called zombie threads for a reason. Nobody wants to see one. Frowned on in almost every forum on the Internet because it just clutters things up to no purpose. Unless you are pulling it up for a very specific reason, with something useful to contribute, old threads are best left in the grave.

Don't sweat it. It's a common newbie mistake. Search engines don't care about dates, only content. If you use the built-in search functions, there is an option to specify age of posts, but I doubt if many people use that.

But every post has a date, and it's a good practice to check it before posting a reply (see below), especially when finding a thread via search. Another contributor to zombie threads is the "related threads" feature that is on by default. It automatically brings up search results as "related threads" below the thread you are reading, and it's really easy to mistakenly drop down into one of those threads when you 're scrolling down a thread. So you think you are replying to the thread you were reading, but you are actually replying to a completely different (and usually OLD) thread. Very confusing and frustrating. It's a good idea to go into your settings and turn that feature OFF.