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Jeep stalls after I let off gas

Nyhammer

NAXJA Forum User
Location
Tahoe Vista, CA
So my 96 will stall after I drop to idle from 1500 rpms or more whether in park or while driving. Cleaned the iac and installed new crank sensor. Starts fine in goes straight to 800 rpm idle and will idle all day but as soon as I get over 1500 and then let off the gas it will die. TPS is about a year old. Iac was still pretty shiney, just a lil carbon on the very tip. Suggestions? Also now trans isn't shifting properly.
 
Make sure to buy a factory Mopar TPS sensor. The junk box store brand sensors last a year then fail. They are all made in China.
 
Hey, just wondering was it throwing any codes? my 98 4.0 intermittly will fire up and die if i dont keep it throttled at or above idle on the pedal. once i put it in drive it will idle and run fine and remain idling if i take it out of gear.


thanks Henry
 
..... my 98 4.0 intermittently will fire up and die if i dont keep it throttled at or above idle on the pedal. once i put it in drive it will idle and run fine and remain idling if i take it out of gear.

I would suspect low battery voltage.

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) when the battery goes bad and needs replacing, (4) when the alternator is not properly charging the battery, (5) or when poor battery connections result in a voltage drop at the PCM or poor battery charging. Loose, corroded, or damaged battery cables or ground wires may also cause or contribute to the problem.

A faulty Coolant Temperature Sensor may also cause similar symptoms. Testing of the CTS is recommended as part of the diagnostics. A poor ground at the ignition coil can also cause similar symptoms.

The reboot 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. (3) The ECU will usually relearn the idle settings after a short period of driving and the engine will start and idle normally.

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 or connectors and replace as needed. Copper wires should be copper color, not black or green. Do the same for the grounding wires from the starter to engine block, the ground wires at the coil, and the ground wires from the battery and engine to the Jeep's frame/body. You must remove, scrape, and clean until shiny, the cable/wire ends, and whatever they bolt to. Jeeps do not tolerate low voltage, bad connections, or poor grounds.

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. Handheld testers are very inaccurate and will usually pass marginal alternators. 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 for smooth starts.
 
Thanks for the info Tim. This is a recent purchase and a somewhat neglected XJ. I've gone over the obvious nasty wiring but yes, grounds need checked as well as testing batt and alt. Solid feedback impossible now after finding a "mashed" gear segment of the flex plate after a starter drive miss-mesh. Debating a trans pull now instead :( and a related thread.
 
My 96 would do that, turned out to be gunk in the IAC. The gunk would be stiff until it warmed up.
Low battery/alternator voltage will also cause the IAC to be sluggish.
Could be one or the other or a little of both.
 
I'm also having the same issue. With NO LINK to PCM mixed into it. I did change the MAP & CPS with Mopar sensors. Cleaned all the grounds in the engine bay and till not luck.
 
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