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Tiny
TQB
  • MEMBER
  • 1993 DODGE DYNASTY
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 176,000 MILES
1993 dodge dynasty 3.0 stalls when foot off the gas pedal. Already changed battery and fuel pump. Alt is charging at 14.5 volts.
Monday, July 11th, 2011 AT 5:42 PM

7 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 33,873 POSTS
The Fuel pump has nothing to do with that. When you disconnected the battery the Engine Computer lost its memory and has to relearn "minimum throttle" before it will know when it must be in control of idle speed. It also might not give you the normal "idle flare-up" to 1500 rpm when you start the engine. To meet the conditions for the relearn to take place, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the brake or gas pedals.
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Monday, July 11th, 2011 AT 6:28 PM
Tiny
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I have never heard of such a thing. Prior to it doing this the water pump and timing belt was replaced. I know its timed correctly as it is an interference type motor and the wrong timing set would be catastrophic. Besides I have driven the car since since belt and pump were replaced. This started when the battery had went totally dead in car. I replaced the battery and the car wouldn't idle anymore. But I will try your suggestion. I appreciate the info.
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Monday, July 11th, 2011 AT 10:23 PM
Tiny
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The 3.0L is not an interference engine so you don't have to worry about valve damage. My daily driver is an '88 Grand Caravan with 379,000 miles. The timing belt has been replaced only once because the water pump was wobbling so badly I was measuring water usage by the mile instead of by the day!

I also have a '93 Dynasty with only 4,200 miles. When I plug in the smaller battery cable once every other year to drive the car, it starts fine but you can feel the idle is too low at stop signs. After coasting off one exit ramp, it is fine.
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Monday, July 11th, 2011 AT 10:42 PM
Tiny
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I tried what you advised, (albeit on jack stands instead on the road) it worked perfectly! After about 5 min at 55 mph I let off the accelerator and it idled perfectly. Thanks a lot. You are a god among men. By the way I apologize for my doubt as I am a motorcycle tech and not a car tech.
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Monday, July 11th, 2011 AT 11:58 PM
Tiny
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Very happy it worked but that surprises me that it worked on jack stands. The way it works is the Engine Computer wants to see high manifold vacuum for at least seven seconds. You'll get high vacuum after snapping and releasing the throttle but not for seven seconds. The computer knows from the speed sensors that the car is moving, but the only way the vacuum can be high for that long is if the car is coasting. When the voltage from the throttle position sensor remains steady during coasting, it knows your foot is off the gas pedal. At that point it memorizes the reading from the TPS. Any time after that when it sees that same voltage, it knows it has to be in control of idle speed.

Be thankful this wasn't a Volkswagen. Disconnecting the battery on them requires a tow to the dealership to have numerous computers unlocked before it will come out of park or increase engine speed, if the engine even starts.
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Tuesday, July 12th, 2011 AT 12:07 AM
Tiny
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I also own a 93 volvo 940 turbo if you know anything about them and want to share some more of your knowledge. I'll start a new thread I have some front end issues with it.
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Tuesday, July 12th, 2011 AT 1:12 AM
Tiny
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Actually, I'm not a Volvo expert, but suspension and alignment and electrical are my two main specialties.
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Tuesday, July 12th, 2011 AT 7:46 AM

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