97 Wrangler TJ Idle and Power Loss - JeepForum.com
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post #1 of 20 Old 04-03-2020, 02:19 PM Thread Starter
jking97
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97 Wrangler TJ Idle and Power Loss

I have a 97 TJ. It has become hard to start and runs rough (idle and driving until rpm's reach 1500 -1700). This is always when it warms up. If it won't start I have to wait for the temp to get down to 150. I have replaced the Cam Shaft Sensor, Plugs, wires, and Coolant Temp Sensor. Not sure the direction to go next. Once started and driving if it is running rough (sputter and little power) once I hit the above rpm's it takes off and runs normal. Need a fix, getting very annoying.

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post #2 of 20 Old 04-03-2020, 02:31 PM
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I have been chasing a similar issue with my 98. Starts normal. Before it gets warm it starts sputtering. Turn it off and restart and its gone. No error codes, nothing. Runs great in fact.
post #3 of 20 Old 04-03-2020, 02:58 PM
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for both posters,

It is best to start a NEW thread and give details you know year, model, engine; trans CODES. It is suggested you use a SCANNER to check codes.

Ideally a scanner would be where to start, codes and live data, NO scanner -

Might want to inspect plugs, look for running rich, leaking injectors.
Fuel pressure and fuel pressure drop KOEO.
Another idea- did this condition start after a repair, modification, add on, or lending vehicle to a teenage ?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #4 of 20 Old 04-04-2020, 04:13 AM
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Quote:
Originally Posted by jking97 View Post
I have a 97 TJ. It has become hard to start and runs rough (idle and driving until rpm's reach 1500 -1700). This is always when it warms up. If it won't start I have to wait for the temp to get down to 150. I have replaced the Cam Shaft Sensor, Plugs, wires, and Coolant Temp Sensor. Not sure the direction to go next. Once started and driving if it is running rough (sputter and little power) once I hit the above rpm's it takes off and runs normal. Need a fix, getting very annoying.
Might want to try unplugging and measuring the resistance of the crank sensor between the B and C pins of the connector. It should be over 10K ohm. Sometimes they can cause problems when hot if they are on the way out. Also might be worth checking fuel pressure, as jtec suggests.


Quote:
Originally Posted by [email protected] View Post
I have been chasing a similar issue with my 98. Starts normal. Before it gets warm it starts sputtering. Turn it off and restart and its gone. No error codes, nothing. Runs great in fact.
This is typical of a bad heater in the upstream O2 sensor. Unplug the sensor and see how it runs. If it runs fine with the sensor unplugged, replace the sensor. NTK were OEM and therefore recommended. Bosch cause problems for some so are generally avoided.
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post #5 of 20 Old 04-04-2020, 07:45 AM
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Basic Jeep troubleshooting:

1) Make sure all of the tune-up parts are fresh. Test the ignition coil. Clean the Idle Air Controller, Throttle Body, and add some fuel injector cleaner to the next two gas tank fill-ups.

2) Remove, clean, inspect, and snug all the engine bay ground locations and all the engine bay wire plugs. Look for corrosion, damaged, chafed or melted wire insulation, failed wire splices, and bent or pushed back wire plug pins.

3) O2 sensors have service life of about 125,000 miles. Test the O2 sensors and O2 sensor fuses. Inspect O2 sensor wires/plugs for corrosion, chafed or melted wire insulation, and bent or pushed back wire plug pins.

4) Test the OBD engine sensors. Replace any engine sensors that do not pass testing. ALWAYS buy genuine Jeep engine sensors and NTK O2 sensors. Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a "Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep engine sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts. Cheap parts are cheap for a reason.

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post #6 of 20 Old 04-04-2020, 12:20 PM Thread Starter
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As a quick solution I replaced the upstream 02 Sensor with an NTK. Drove for a while. At first it ran extremely rough, (not sure if that is normal) but improved. I don't think is 100% yet. So time will tell if this is the fix. I'll post after a few days of driving.
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post #7 of 20 Old 04-04-2020, 12:44 PM
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Reboot the PCM to clear the adaptive memory of any bad data from faulty engine sensors.


This procedure will erase the 1996+ OBD-II "Adaptive Memory" stored inside the PCM and allow a new "Adaptive Memory" to be developed. After performing this procedure the PCM will re-learn and store into Adaptive Memory your engines performance characteristics. Perform these steps exactly as they are written, in the order they are written. This will cause the adaptive memory in the PCM to be erased and cause the PCM to go into Fast Learn adaptive mode.

Disconnect the POSITIVE battery Terminal clamp and firmly touch it to ground ( not the battery negative terminal ) for 30 seconds. The engine block or the A/C compressor pump will work as a ground. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory).

Reconnect the Battery Cable
Turn Ignition Switch to the "ON" position but DO NOT start the engine
Turn Headlight "ON"
Turn Headlights "OFF"
Turn Ignition Key "OFF"
 
The PCM Adaptive memory has now been flashed, or erased from the PCM. When you start the engine it will be running off pre-programmed data tables that come with the PCM from the factory. When you get the engine up to operating temperature the PCM will start to collect and store new data for the Adaptive Memory.

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post #8 of 20 Old 04-05-2020, 02:34 AM
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Quote:
Originally Posted by jking97 View Post
As a quick solution I replaced the upstream 02 Sensor with an NTK. Drove for a while. At first it ran extremely rough, (not sure if that is normal) but improved. I don't think is 100% yet. So time will tell if this is the fix. I'll post after a few days of driving.
The O2 sensor isn't used at first as it is not accurate until hot. It won't have been the cause of hard start or initial rough running issues.
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post #9 of 20 Old 04-05-2020, 07:27 AM Thread Starter
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I will clear the PCM this morning. After installing the new 02 sensor, oddly, last night I finally got the CEL with a code of P0171 (lean mixture). I'm confused by this unless it is in a correction mode.
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post #10 of 20 Old 04-05-2020, 09:42 AM
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Maybe the fuel pump is weak. Time to get the pressure checked.
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post #11 of 20 Old 04-05-2020, 09:53 AM
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As CJ Tim suggested clear the RAM (Adaptive Memory) The new o2 sensor MAY be conflicting with stored data.

If a code appears let us know.

PS you never did say - do you have a scanner so we can look at live data?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #12 of 20 Old 04-05-2020, 10:06 AM
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I've swapped O2 sensors before I even new about the adaptive memory reset. It won't do any harm resetting the adaptive memory but it's not necessary.


An aged fuel pump, crank sensor or coil could cause problems when the get warm. A bad crank sensor or coil could certainly prevent starting when hot. Some times old coils can crack but more noticably on the engine side from the few pics I've seen so hard to see without removing it.
Coil resistance can be checked. Spec is 0.95-1.15 for the primary and 11,300-15,300 ohms IIRC.
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post #13 of 20 Old 04-06-2020, 09:42 AM Thread Starter
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I'll check on the suggestions. I did clear the codes (with battery disconnect and I do have a scanner). Ran rough for a while then the CEL came on. Did a scan and got P0123 and P0505. Still having an issue starting when hot. When temp drops to 150 it starts right up.
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post #14 of 20 Old 04-06-2020, 11:55 AM
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TPS and IAC codes. I wonder if the IAC is sticking when hot. With those codes I think it's worth cleaning up the throttle body and IAC. TPS might need checking with a meter to see if changes smoothly with throttle position or has any bad spots.
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post #15 of 20 Old 04-06-2020, 02:35 PM
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im glad you got the codes but i was thinking the tps and related stuff since its only on warmup and low rmp makes the thinks those items instead of the other items that would generally be bad all the time or get worse with heat. you may also check the Maf just cause it affects everything under the sun but yes if you have live data you can test the tps for good signal and to see what the computer says its at. small (Very small) chance you may just have to reset the tps to get it to read the position on the pedal correctly (also need to do this if a new tps is put in) on a side note i really wish cars came with more useful gauges in them
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