99jeepc4door

Ok I can't figure this out maybe you all can help I have a random stalling problem at idle it seems to act up when warm no codes thrown can come to a stop and you can sometimes hear the motor idle down and if you put your foot on the gas to catch it it will rev really high and than idle down and run like crap .. If it does stall the only way it will start is to hold the gas Pedal to the floor and crank the motor and will start up I've cleaned the iac (bullet looking sensor ) and haven't had a change even after a comp reset also checked fuel pressure and it holds steady at 50 ne ideas would help greatly been on here for a long while but first time asking for help

JeepingDan

Moved to tech so you will get better responses.

99jeepc4door

Thanks. For moving it

tjwalker

There are a few possibilities but you should LOAD TEST your battery first. Any parts store will do this for you for free.

A marginal battery can raise fits with your engine management system and create stalling/idling problems. I answer about 3 threads a week at least on this. And yes, you ABSOLUTELY can have a battery strong enough to start the engine, but marginal enough to give you idle symptoms. Very common actually.

After verifying battery, try cleaning your idle air control and throttle body. They get carboned up over time and miles.

99jeepc4door

I've cleaned the throttle body and no changes I'll take my battery in on Monday any more ideas

ts210021

If it helps at all I had the same problems this week and I ended up being my battery. Good luck

99jeepc4door

Any other ideas

Gee oh Dee

Was the battery tested?

99jeepc4door

Battery tested good

tjwalker

You mentioned you cleaned the throttle body. You also need to clean the Idle Air Control.

They get carboned up and can malfunction.

99jeepc4door

Cleaned the iac and tested it when out and turned key on and off the iac moved in and out

kissthis66

"You also need to clean the Idle Air Control." noob question, where is this located/whats it look like? I have a similar issue.

tjwalker

Next up is verifying throttle position sensor. Here is more. The testing procedure is for all TPS from 91-01.
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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.