Doug_the_chug

I have followed countless threads on IAC cleaning and replacement and TPS adjustment and replacement but nothing seems to fit my case. 5 months ago I had the rough low idle problem, so following excellent advice from this forum I cleaned the throttle body, IAC and removed the TPS mistakenly. The problem went away and my Cherokee was running clean as a whistle until about a month ago. Now after the engine is warmed up when I come to a stop or when the Jeep is in park the idle is super low at 200 RPM and almost konks out. So investigating under the hood I cleaned up a few things including disconnecting my battery and cleaning my connection. That fixed the problem for a few weeks, but then the problem came back. Then I got the battery checked - it was fine, but the problem once again went away for a week or so and now it's back. I could be wrong, but I'm thinking that the power cycle on the system resets something and makes the Jeep run good until a calibration takes place? Could this be a faulty or malconfigured IAC or TPS? Any info would be appreciated.

Chickenfloss

What year is the vehicle?

Doug_the_chug

2001 Jeep Cherokee Sport, Inline 6 Automatic

Chickenfloss

There is a relearn done after the battery has been disconnect for a length of time. It runs in somewhat of a default setting called open loop where fuel/air mixtures are preset to a safe amount as well as idle, etc, etc. After a few minutes of driving it 'relearns' everything based on environmental condition with your motor from information given via sensors like the O2's and so on.

I would check for vacuum leaks and possibly look into map sensor or check it's connection for corrosion. These can be the cause of some weird idle problems and low idle definitely can fall into it's jurisdiction. If the map sensor connection doesn't look corroded, you may still try spraying some electrical component cleaner on it to coat it to prevent future corrosion and try unplugging it and plugging it back in a few times to scratch up the contacts a bit. Also, just because it looks good doesn't mean it's not bad. They can simply internally fail and sometimes fail to throw an error code. There may be a way to test it, but I am unsure what the procedure would be for your jeep. Here is a link that looks like it may be applicable for you. http://www.cherokeetalk.com/forum/f6...rocedure-1261/

This link was passed onto me by someone here and was extremely helpful.
http://www.go.jeep-xj.info/HowtoECUcodes.htm

Your procedure and codes would be listed in the bottom of the page. Although you don't see a CEL you may still have codes being stored. You can check them by following that table or a local parts store may pull them for free for you. It could give you more of a hint on where to start. These codes may/probably will be wiped after resetting from unplugging the battery, so check them now or drive it awhile before checking. Checking just after reset would probably do you no good.

Doug_the_chug

Correct me if I'm wrong, but if there was a vacuum leak wouldn't it show itself regardless of whether the battery has been disconnected?

I disconnected the connectors and they all are clean and show no signs of corrosion

Chickenfloss

Usually but not necessarily. When in open loop the system runs rich to prevent a lean condition which could royally screw your motor over. As a result a little extra air into this rich environment may let it run mostly normal and not be noticeable until sensor data is collected and then restored to a normal operating condition which now has air coming in that isn't calculated for.

Besides it's good to check your hoses from time to time anyway ;p May prevent future problems and it's a free place to look without the cost of a sensor just yet.

hankthetank

Is there a power latch (IAC) relay on 91 and up?

Doug_the_chug

Checked the vacuum...no leaks. Checked the MAP sensor and its electrical connection and ground and all is good. Checked the voltages on the TPS and at an idle the TPS voltage reads 1.0 Volts. Any ideas guys?

Doug_the_chug

I know that the O2 sensors have never been changed, could this be the issue? May be I should just unplug my battery every week

Chickenfloss

Well, if you are at high mileage already then you may as well replace the o2's it will have to be done eventually anyway so it couldn't hurt.

What is the TPS voltage open just out of curiosity...

tjwalker

Here is how to properly verify the throttle position sensor on your 2001. I'd highly recommend it.
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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.

Doug_the_chug

The voltage of the TPS is at 1.0 at idle and is less than 4 volts at WOT. I just disconnected my battery once again to temporarily fix the issue A permanent fix would be better and appreciated if anyone has any ideas.