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Steve Hiltpol
Dodge Dakota
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2/05/2008
07:14:04
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 Subject: RPM fluctuates
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Message:
I have a 2000 x 4.7 automatic. Once engine has warmed up, RPM's will increase by 200-300 at all speeds : while idleing at a stop light, while going 70 with cruise control, and just driving down the street. RPM's only stay high for a couple of seconds, then drop back to normal. Then the cycle repeats. Seems to be worse in hot weather.
Did a diagnostic scan, but no error messages.
Any ideas what to check ?
Thanks
Steve
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Kowalski
GenIII
2/05/2008
07:30:07
| RE: RPM fluctuates
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Message:
One possibility would be the throttle position sensor (TPS). If it sends a wrong signal, the PCM could be unlocking the torque converter; causing rpm to vary.
Lead, follow, or get out of the way
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.boB
Dodge Dakota
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2/05/2008
10:44:36
| RE: RPM fluctuates
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Message:
Mine used to do that. Only on a steady cruise on relativly flat ground - like I70 in KS. Kinda annoying. I cleaned the TB and replaced the TPS, and that stopped it.
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Steve Hiltpol
Dodge Dakota
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2/05/2008
11:23:13
| RE: RPM fluctuates
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Message:
OK guys, thanks. I'll check the throttle body and position senser this weekend.
Appreciate the feedback.
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Steve Hiltpol
Dodge Dakota
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2/11/2008
08:44:36
| RE: RPM fluctuates
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Message:
Cleaned the throttle body and the idle air control motor, and checked the TPS and it seems to be working OK. Changed the plugs as well.
So far, the RPM fluctuation does not appear to be a problem.
Thanks for the help.
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fgaffer
Dodge Dakota
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2/11/2008
10:51:45
| RE: RPM fluctuates
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Message:
also it might have something to do with the A/C cycling on defrost and using it more in the summer.so if it happen again.try turning off the defrost an A/C control.
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Steve Hiltpol
Dodge Dakota
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2/11/2008
15:53:04
| RE: RPM fluctuates
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Message:
It happens even with the A/C off
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TexasTodd
Dodge Dakota
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2/11/2008
17:22:42
| RE: RPM fluctuates
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Message:
Steve,
I don't think it's your a/c compressor either, but I think the gaffer is referring to your a/c compressor cycling on and off when it's only on defrost setting. Even if the little snowflake light isn't lit, it still cycles on and off when in defrost mode.
Good luck and keep us posted on this.
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marc
Dodge Dakota
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2/11/2008
21:31:13
| RE: RPM fluctuates
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Message:
I had the same problem for a while and it sounds like you did all the same things I did. It fixed mine instantly and I haven't had a problem at all since.
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gaffer
Dodge Dakota
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2/11/2008
23:21:13
| RE: RPM fluctuates
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Message:
thanks for the extra help TEXAS TODD
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daddio
Dodge Dakota
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2/12/2008
08:46:29
| RE: RPM fluctuates
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Message:
did you use a voltmeter to check the TPS? it might "feel" right but unless you actually put a meter on it you won't know.
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Steve Hiltpol
Dodge Dakota
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2/13/2008
12:25:05
| RE: RPM fluctuates
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Message:
When I had the throttle body off, i checked the leads with an ohmmeter. When I opened the closed the throttle, the resistance would increase and decrease accordingly, but will check the voltage this weekend. Supply voltage or wiring could be bad.
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daddio
Dodge Dakota
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2/13/2008
12:50:43
| RE: RPM fluctuates
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Message:
the way i would check it is to turn the key on, truck not running. back probe middle wire on the connector and to ground. @ idle anywhere form .5-.75 vdc is good then run to wide open throttle and should get about 3.5- 4.8 vdc. now, the real test, when you release the throttle back to idle, you should get the exact same reading you got the first time at idle. also, whtch for any serious jumps in the readings between idle and full throttle. could have a bad spot.
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Steve Hiltpol
Dodge Dakota
JOIN HERE
2/26/2008
16:21:03
|  RE: RPM fluctuates
IP: Logged
Message:
Cleaned throttle body and IAC motor, replaced throttle position sensor, and for good measure, changed spark plugs.
No more RPM fluctuation.
Thanks for the help.
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