I have a 2000 cherokee sport 4L, and when its cold out (Michigan :/) it likes to idle rough when I start it. It usually stays this way for several minutes, even when I begin driving. This makes it a pain when im in a hurry as I have to have one foot on both pedals so I can switch to neutral at stop signs and keep gas on it so it doesnt die. Over the summer there are no problems. I've cleaned the throttle body, but not much more than that. The only other replacement was over the summer, my Crankshaft position sensor suddenly died so I put a new one in. I've heard that a bad cps can cause this, but the idling when it is only cold makes me think its a feul/air ratio problem. Also it hadnt been cold enough to see any posible improvements. Any ideas? Help would be greatly appreciated!

 

Test the throttle position sensor to make sure it has the correct resistance. If not, replace it. Also do a tune up if you're past due, plugs, wires, cap, rotor

 

^ Very good advice.

Do a fuel filter as well. Also, get the charging system tested, just for kicks & gigglys.

 

Tested resistance of my tps, and it matches the new one at autozone. I replaced plugs & wires last summer, so I doubt that's the problem. Any other ideas?

 

Fuel filter is next on my list

 

1. I agree that the throttle position sensor is a possibility. Unless you've done the testing I've listed below, it's still in play. You test for a smooth VOLTAGE sweep on this component, not resistance. Best to use an analog meter for this.

2. The 2000 has a distributorless ignition. No wires, cap or rotor. Its a "coil pack" system. Be sure plugs are fresh though. No more than 30k on copper plugs. I recommend NGK copper plugs for the 00-01 XJ. Gap em before installing them.

3. The fuel filter on the 2000 is part of the "fuel pump assembly" located inside of the gas tank. It is not generally replaced UNLESS testing
and symptoms point directly to it.

4. This doesn't sound like a fuel issue to me, but if you get stuck, you can easily verify fuel pressure at the schrader valve on the fuel
rail. For a 2000, you should have 49 psi, plus or minus 5 psi. Look for out of spec or very marginal readings.
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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 acordingly 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 deined acceptable range causing the ECU to incorrectly fuel the engine. This is noticable 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 did check the resistance, so ill look into the voltage tomorrow. Also, when cruising at 70ish my transmission does occasionally slip, so from what I read a bad tps may be to blame also. Thank you for a great walk through, I will let you know what happens.

 

Had the same problem with my 1997 Cherokee Sport. Just changed the throttle position sensor and is running smoother than ever. Thanks for the help.

 

Changes the tps, and the issue seems to be fixed. Thanks for the help!