Jeep won't idle - intermittent problem

Okay, so I've search just about everything I can find regarding this issue, and I can't seem to find anything that matches my particular problem. Hoping you folks can help out.

I've got a 1997 XJ, 4.0, 5 speed, 168xxx miles. The only engine mods I've done include a new-style intake swap from a 2000 grand cherokee, rusty's air tube and cone filter, new fuel rail and injectors from said intake, and new cap/rotor/wires/plugs.

When I start the Jeep, there are some instances where it will fire, then sputter out and die. When I got to restart it, it will crank indefinitely unless I depress the gas pedal a little bit. At that point, it will stumble to life, but will only remain at idle if I keep the gas pressed. If I release the gas very slowly, I can usually get it to catch and hold idle by itself (after ~10 seconds of holding it at idle myself). At this point, it will idle just fine.

Now, once I start driving and then remove the load from the engine (such as clutching in coming up to a stop sign), the revs will drop WAY down, usually around 50-80, and the Jeep will usually stall out. Restarting procedure is the same as above, although usually takes a lot longer to get it to fire.

Once the Jeep is warmed up, this problem seems to go away. It only seems to be there when the Jeep is in a semi-warm state. I've tried unplugging the coolant temp sensor to bypass it to see if it's the problem, but this didn't fix it.

I've replaced the idle air controller in the last month, so that part is good. Any ideas what might be problem?

ras97XJ said:

... go to restart it, it will crank indefinitely unless I depress the gas pedal a little bit. At that point, it will stumble to life, but will only remain at idle if I keep the gas pressed.

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Load Test the battery and alternator.


For 1996+ Jeeps, the OBD-II engine computer (ECU/PCM) re-boots, and the idle settings are deleted, when you: (1) let the battery run down by leaving the lights or radio on, (2) disconnect the battery for an extended period of time, (3) or when the battery goes bad and needs replacing.

Your symptoms are: (1) having difficulties starting the engine without depressing the gas pedal, and (2) the engine will have a low idle and probably stall unless you keep your foot on the gas pedal.

The ECU will relearn the idle settings after a short period of driving and the engine will start and idle normally. Loose, corroded, or damaged battery cables or ground wires may also cause or contribute to the problem. Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables and replace as needed. Do the same for the grounding wires from the battery and engine to the Cherokee's frame/body.

If the symptoms reoccur, you need to have your battery and/or the alternator load tested at a repair shop or auto parts store. This is usually a free service they offer to bring in potential customers. Even with low battery voltage, the engine will start, but the ECU can re-boot multiple times and a new battery may be required.

Cleaning the Idle Air Controller (IAC), regular tune-ups, and using fuel injector cleaner should be part of your routine preventative maintenance.

Thanks for the information! I've been a little suspect of the battery going bad for a little while now, but I'll check all of the connections you mentioned before buying a new one.

The alternator is less than a month old, so hopefully that's not the issue.

I've also gone through a similar deal recently with my '96. I knew I had a marginal Throttle Position Sensor, so I bought a new one, and a new IAC to go with it. All I got was two weeks of hell. Finally it lit the CEL on Saturday, TPS. A 'new' one from the JY, and all is well! Unfortunately, you're stuck looking for one from a '97, as the plug changed after '96, and a '98 is a different part #.

#1. Clean battery connections and load test the battery as mentioned. A marginal battery can result in the symptoms you are seeing.

#2. Battery check out? Test your throttle position sensor.

Four years later but no answer as to what was the fix! Would be a much appreciated addition to the thread if we knew what was going on. Did it end up being the battery? The TPS?

Thank you

rorytothemax said:

Four years later but no answer as to what was the fix! Would be a much appreciated addition to the thread if we knew what was going on. Did it end up being the battery? The TPS?

Thank you

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If you're looking for a "silver bullet" cure for this issue, there is none.

Too many things can cause this, from dirty throttle body, failed TPS, alternator, battery, IAC, old tuneup parts, ad infinitum.

Are you having an issue like the original poster was?