I have a 1998 JGC 4.0 liter and it's been acting up recently.
Every so often it wouldn't start. The engine would turn over, but it wouldn't actually start until the 2nd or 3rd try. The weird thing is that while the engine is turning, you can press the accelerator, and the car would start and rev to the appropriate rpm level, but if you let off, instead of idling, it would just die. It would do this like once a week. This morning as I was going to work it did the usual, only this time it wouldn't start at all. Still did the rev thing when I pushed the throttle, but wouldn't idle. So this afternoon, I'm kinda giving it a visual inspection but don't notice any leaks or anything unplugged. So I start it and rev it to keep it from dying. I leave it at about 2,000rpms for about 30 seconds then slowly let it down and it idled just fine. So I tried to mess it up by blipping the throttle but it idled fine. Turned it off....turned it on and it cranked right up. Any ideas?

My GC's both did the same thing when the battery needed to be replaced. The voltage would drop too low and mess with the computer when I would start the engine. I would have to drive it for a couple of miles, so the computer could relearn, then it would run fine.

My GC's both did the same thing when the battery needed to be replaced. The voltage would drop too low and mess with the computer when I would start the engine. I would have to drive it for a couple of miles, so the computer could relearn, then it would run fine.

Thank you, I will change the battery this week.

I have a 1998 JGC 4.0 liter and it's been acting up recently.
Every so often it wouldn't start. The engine would turn over, but it wouldn't actually start until the 2nd or 3rd try. The weird thing is that while the engine is turning, you can press the accelerator, and the car would start and rev to the appropriate rpm level, but if you let off, instead of idling, it would just die. It would do this like once a week. This morning as I was going to work it did the usual, only this time it wouldn't start at all. Still did the rev thing when I pushed the throttle, but wouldn't idle. So this afternoon, I'm kinda giving it a visual inspection but don't notice any leaks or anything unplugged. So I start it and rev it to keep it from dying. I leave it at about 2,000rpms for about 30 seconds then slowly let it down and it idled just fine. So I tried to mess it up by blipping the throttle but it idled fine. Turned it off....turned it on and it cranked right up. Any ideas?

11/23/05 Hi..I'm new to the forum so hi everyone. My JGC has done the exact same thing as yours and I did the same as you by idling it with the gas pedal. One of the codes that came off of my PCM (computer) was for the ASD relay. After purusing through the haynes manual it seems there are several possible causes including Camshaft Position Sensor and the Crankshaft Position Sensor or any of the wiring connecting them to the PCM. Seeing that the PCM controlls the firing order of the ignition, a short or malfunctioning of any of the numerous sensors or relays can cause trouble with how the engine runs. Did your check engine light come on?

11/23/05 Hi..I'm new to the forum so hi everyone. My JGC has done the exact same thing as yours and I did the same as you by idling it with the gas pedal. One of the codes that came off of my PCM (computer) was for the ASD relay. After purusing through the haynes manual it seems there are several possible causes including Camshaft Position Sensor and the Crankshaft Position Sensor or any of the wiring connecting them to the PCM. Seeing that the PCM controlls the firing order of the ignition, a short or malfunctioning of any of the numerous sensors or relays can cause trouble with how the engine runs. Did your check engine light come on?


Thank you for your reply, how do you check for codes from the PCM on a 98? No, my check engine light does not come on when I'm having this problem. It was suggested that I change my battery, I have not yet because the volt gauge on the dash reads around 10-11 without the engine running and 13-14 with it running.

Thank you for your reply, how do you check for codes from the PCM on a 98? No, my check engine light does not come on when I'm having this problem. It was suggested that I change my battery, I have not yet because the volt gauge on the dash reads around 10-11 without the engine running and 13-14 with it running.

11/23/05 Hmmm...with the battery only reading 10-11 volts at start up it might be worth it to have the battery tested if you think you need to replace it. You could also be dealing with some corroaded battery termimals which would you give you a lousy ground so I'd check them too. With 13-14 volts reading with the engine running the Alternater should be fine. Come to think of it when mine did what yours did I don't think mine had an "check engine" light come on either. Mine only did this once and it hasn't repeated. Anyway, "Auto Zone" will test your PCM (computer) for free. They might be able to test your Battery too although you might have to disconnect one of the terminals. (Note; all the PCM engine trouble codes are listed in the Hayes Repair Manual )

11/23/05 Hmmm...with the battery only reading 10-11 volts at start up it might be worth it to have the battery tested if you think you need to replace it. You could also be dealing with some corroaded battery termimals which would you give you a lousy ground so I'd check them too. With 13-14 volts reading with the engine running the Alternater should be fine. Come to think of it when mine did what yours did I don't think mine had an "check engine" light come on either. Mine only did this once and it hasn't repeated. Anyway, "Auto Zone" will test your PCM (computer) for free. They might be able to test your Battery too although you might have to disconnect one of the terminals. (Note; all the PCM engine trouble codes are listed in the Hayes Repair Manual )

Thank you for the info... I'll run it up to Autozone in a couple of days. Have a great Thanksgiving.

Thank you for your reply, how do you check for codes from the PCM on a 98? No, my check engine light does not come on when I'm having this problem. It was suggested that I change my battery, I have not yet because the volt gauge on the dash reads around 10-11 without the engine running and 13-14 with it running.


On your 98 model you cannot check the codes yourself, I dunno why jeep did this but this is the only year that you are not able to do this on.

Check the Battery with a digital voltmeter, you should have at least 11.5 volts with the engine off. If your voltage is lower then that then the battery is weak and not holding a full charge. You may want to replace.

Wow, sorry I didn't read your first post until now.

Your symptoms are caused by a bad IAC (Idle Air Control) Valve.

"The throttle body has an air control passage that
provides air for the engine at idle (the throttle plate
is closed). The IAC motor pintle protrudes into the
air control passage and regulates air flow
through it. Based on various sensor inputs, the
powertrain control module (PCM) adjusts engine idle
speed by moving the IAC motor pintle in and out of
the air control passage. The IAC motor is positioned
when the ignition key is turned to the On position."


With that said, the problem with you IAC, when you turn the key the pintle is not moving out of the hole to allow air to get by to start the jeep, and when you push on the gas pedal it allow air to get into the engine and then after a few seconds the IAC opens and allows it to idle.

I had this same exact problem about a year ago, I replaced my IAC Valve and it took care of the problem, REMEMBER TO DISCONNECT THE BATTERY BEFORE REMOVING/REPLACING THE IDLE AIR CONTROL VALVE.

you must disconnect the battery or you will not get any change, when I first replaced mine it didn't help still was doing the same thing, so I figured it was abad part from autozone, well took it back and got a new one, and when I was removing it I remembered that I forgot to disconnect the battery before replacing the last one, so I made sure to disconnect the battery this time and I have not had a problem since.

Wow, sorry I didn't read your first post until now.

Your symptoms are caused by a bad IAC (Idle Air Control) Valve.

"The throttle body has an air control passage that
provides air for the engine at idle (the throttle plate
is closed). The IAC motor pintle protrudes into the
air control passage and regulates air flow
through it. Based on various sensor inputs, the
powertrain control module (PCM) adjusts engine idle
speed by moving the IAC motor pintle in and out of
the air control passage. The IAC motor is positioned
when the ignition key is turned to the On position."


With that said, the problem with you IAC, when you turn the key the pintle is not moving out of the hole to allow air to get by to start the jeep, and when you push on the gas pedal it allow air to get into the engine and then after a few seconds the IAC opens and allows it to idle.

I had this same exact problem about a year ago, I replaced my IAC Valve and it took care of the problem, REMEMBER TO DISCONNECT THE BATTERY BEFORE REMOVING/REPLACING THE IDLE AIR CONTROL VALVE.

you must disconnect the battery or you will not get any change, when I first replaced mine it didn't help still was doing the same thing, so I figured it was abad part from autozone, well took it back and got a new one, and when I was removing it I remembered that I forgot to disconnect the battery before replacing the last one, so I made sure to disconnect the battery this time and I have not had a problem since.

Thank you. Is the IAC easy to change? I see that they sell it at Autozone for $46.00

Yes it is real easy to change.

If you email me I will give you the sheet for the replacement of the IAC Valve along with pics of it's location.

Joe
dksob81@hotmail.com

Yes it is real easy to change.

If you email me I will give you the sheet for the replacement of the IAC Valve along with pics of it's location.

Joe
dksob81@hotmail.com

Great! Will do

Chris