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fot80
Dodge Dakota
12/22/2001
04:42:57
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 Subject: fluctuatin rpms
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Message:
I was driving home late last night and I going down a steep hill I threw the truck in neutral. As I was coasting down I noticed that the rpms would fluctuate from around 550 to 950. Is this normal? This does not happen if the truck is sitting still.
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Troy
Dodge Dakota
12/22/2001
08:56:44
| RE: fluctuatin rpms
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Message:
Sometimes if you have the cruise control set and put it in neutral, the rpm's will fluctuate. Did you have the cruise set before doing this?
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JimB
GenIII
12/22/2001
09:09:35
| RE: fluctuatin rpms
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Message:
What motor do you have and how many miles? Around 60K, I noticed this occurring on my 5.9 Durango, only with cruise engaged, travelling between 60-70 MPH. The RPM's would go up and down. Was driving me crazy. After posting my problem in another forum, I learned other's were experiencing this too. Majority of them said they replaced the Throttle Position Sensor and fixed the problem. My mechanic performed throttle body service on it (instead of replacing the sensor) and it fixed the problem. He said there was a high amount of "gook" built up in there. Good luck - Jim
99 SY 3.9 Dakota Sport
99 PB 5.9 Durango SLT
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Bruce P.
Dodge Dakota
12/22/2001
19:46:25
| RE: fluctuatin rpms
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Message:
This is perfectly and completely normal operation.
I first reported it in the edmunds forms several years ago.
The ECU (EngineControlUnit...AKA computer) is trying to "learn" how to idle under the new conditions you just threw at it. If you stayed in neutral and came to a complete stop... you would have seen your engine "LOCK IN" to a normal idle as soon as the signal from the speed sensor in the rear differentual stopped pulsing.
The ECU also has "memory banks" in it that stores many different operating conditions and "recalls" the proper engine settings each time the same conditions are encounterd. Apparently you have not coasted in neutral in the past with the VERY SAME external conditions. The Dakota shop manual explains this in gory detail.
BOTTOM LINE:
If you were to coast in neutral long enough, the ECU would "learn" how to idle under those conditions and settle out. (and "remember" the settings for the future until you put it back into DRIVE and change the conditions again)
Please review the archives of the edmunds forums for more info on this phenomia.
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fot80
Dodge Dakota
12/22/2001
20:47:43
|  RE: fluctuatin rpms
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Message:
Thanks a lot Bruce. You've been very helpful. It's nice to know that my engine's working fine.
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SloDak39
Dodge Dakota
12/24/2001
23:26:22
| RE: fluctuatin rpms
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Message:
Mine does that when it is sitting still......mainly when the engine is warming up.......it also seems like it wants to stall whenever i put it in park......
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