Engine stalls

Tiny
C_MARROW
  • MEMBER
  • 1998 JEEP WRANGLER
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 95,000 MILES
Over the past month i've noticed my 98 wrangler started running a little rough - when at a stop light at idle, I could feel a little fluctuation in how smooth the engine would run.
A week ago, when shifting from reverse to drive, the engine stalled. The only way to avoid this is to come to a complete stop, pause, and then put it in drive.
Fearing that is was the transmission, I tried putting it in 1st instead of drive and it stalled immediately.

Had the crank sensor replaced and this did nothing to help. Another mechanic looked it over and said they can't tell what's wrong. My next step is to go to the Jeep dealer, but I'm hoping someone can give me some idea of what is going on before this becomes a $$ pit.
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Monday, June 1st, 2009 AT 11:53 AM

4 Replies

Tiny
JASONRAY
  • MEMBER
No, don't go to the dealer yet. Let me try to help. What about when you go from Drive to reverse? Does it still die? What about when you go from Park to Reverse? Does it ONLY die when you put it in Drive? AND. Does it do it EVERY time>? A couple of things come to mind, considering that it's a Jeep. Not a bad thing, tho. I've put a lot of IAC solenoids on them. That's the little solenoid on the throttle body that controls the idle speed. It has a plunger in it that seats into a hole, or opening in the throttle body. The PCM tells it what to do based on various inputs, such as 'gear selection' on automatic tranny's. If that plunger becomes 'caked' with carbon/soot, then not enough air can get past it to allow the engine to run. It may have a LOW idle speed even in park or may even stall in park or neutral. Usually, removing it and cleaning it will fix it. ALSO, there could be something going 'haywire' in the transmission telling the torque converter to lock up when it's put in drive. This is more of a major problem, tho. I would really like to rule out the IAC solenoid first. When it dies, does it feel like you just 'dumped' the clutch on a 'standard' transmission when you put it in drive? Does the jeep lurch forward and die or does it just stop running? Get back with me with a few of those details and we'll figure it out.
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Monday, June 1st, 2009 AT 3:51 PM
Tiny
C_MARROW
  • MEMBER
I just spent 10 minutes trying to get the jeep to stall and it wouldn't. But came very close several times. Isn't that always the way it goes. Here's what I did find.

The times it has cut out, it was as if the engine was overstrained - like if you put a manual car in 2nd gear from a dead stop. The rpm's go down and then the engine dies.

Doesn't matter if it's drive to reverse or reverse to drive. It drops down to about 300 rpm and shutters for a second and then returns to 750 rpm. I did notice if I'm going forward slowly so that it doesn't go out of the low gear, and then switch to reverse it does the 'near stall' every time. Might be my imagination, but when i'm turning the wheel, it further taxes the engine and makes it come to a near stall.

Sitting at a complete stop, shifting from park to reverse or park to drive or park to 1st it drives the rpm down to a near stall / 300 rpm.

Just sitting still in drive (at a stop light etc) it shudders very slightly every 3-4 seconds.

I don't know if this matters either, but it used to idle in park at about 1500 rpm - now it sits at 750. I've been told the 750 is correct. To my knowledge, nothing was done to the car to have changed this.

Could this just be as simple as plugs and injectors?
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Monday, June 1st, 2009 AT 7:57 PM
Tiny
JASONRAY
  • MEMBER
Probably not. If it was the ignition system (i.E. Plugs and wires, etc.) Or the injectors, it would most likely miss under a load on 1 or 2 cylinders only but probably wouldn't kill the motor. I'm still leaning towards the IAC solenoid. Even more so after the new details. And good job, by the way on getting more specific. If it resembles a 'straining' engine, it could be caused by the IAC solenoid not allowing enough air in to keep the engine running. 750 rpms is correct, not 1500. The PCM tries to keep it at 750 rpms no matter what's happening as long as the throttle is closed. It does this by retracting or protruding the plunger on the solenoid to restrict air or allow more air in. When you're turning the steering wheel, that puts more load on the engine, therefore, the PCM will pull the plunger back some to allow more air in to raise the RPM's slightly to maintain the desired idle speed. Or when the A/C compressor kicks in. Same thing. If there is a lot of build-up on the end of the plunger, the PCM doesn't have any way of knowing it, and it has a preset value stored so it will know where to stop the plunger. These values are called 'steps'. So, to try to sum it up, when the A/C is on, the PCM knows that it needs to adjust the IAC to 'X' number of steps to maintain the correct idle. So it does. However, the buildup on the plunger restricts the air flowing past, so the engine is starving for air. When you put it in gear, the very same principle is utilized. The transmission puts WAY more load on the engine than the A/C or power steering, so the lack of air is magnified several times more, and the motor stalls. I would suggest removing the IAC, and using some strong B-12 Chemtool or equivelent, clean the plunger AND! It's seat inside the throttle body. It only takes 2 'torx' headed screws to remove it from the throttle body. It's really pretty simple. Occasionally, the solenoid has to be replaced but try cleaning it first. Let me know how it turns out.
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Tuesday, June 2nd, 2009 AT 8:19 AM
Tiny
CIVICSIEBP
  • MEMBER
I had the same symptoms as above. I've already replaced the TPS and cleaned the throttle body and IAC sensor. Then I though about replacing the IAC motor and that fixed it. Thanks for the help.
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Monday, April 12th, 2010 AT 8:50 AM

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