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Dan M
Dodge Dakota
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5/26/2008
22:03:24
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 Subject: reving idle when cold
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I have an 02 QC 4x4 automatic. For some time now when the engine is cold, when I start up the truck, it would rev a little. It would mostly idle around 600 rpm but would spike, sometimes as high as 1500 rpm.
I checked with my scanner (auto x-ray 6000 w/ chrysler enhanced OBDII) and noticed the MAP voltage was around 1.3V and would change when the truck would rev. I monitored the TPS and it would stay at a constant .5V. I figured it was not the TPS sensor.
after the truck warmed up and went into closed loop, it would not rev like this.
I wasn't sure if the rev was caused by the map voltage or the map voltage caused the rev., Regardless I changed my MAP sensor (was only $30) and when I first start the truck up it will rev 2 maybe 3 times then stop even if it had not warmed up yet.
I noticed that my vaccum would be fairly constant but would change slightly. Could this 2 or 3 time rev be related to a vacuum issue? I don't think it could because it only does it when cold. Or is this 2 or 3 time rev normal?
truck has just over 90k miles and has a distributorless ignition so it's not wires or cap/rotor. The current plugs (halo) have been in the truck for about 20k miles or so. This weekend I'm going to try to pull the plugs and check them.
- Dan M
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Gr-r-r-r
Dodge Dakota
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5/26/2008
23:16:25
| RE: reving idle when cold
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Dammit man. We need to know what engine you got.
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TexasTodd
Dodge Dakota
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5/27/2008
01:42:43
|  RE: reving idle when cold
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That would be the 4.7l dumb azz.
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Kendall
Dodge Dakota
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5/27/2008
08:19:35
| RE: reving idle when cold
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You said "when I first start the truck up it will rev 2 maybe 3 times then stop"
So the engine revs a couple times then shuts down?
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Dan M
Dodge Dakota
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5/27/2008
12:01:39
| RE: reving idle when cold
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4.7L V8
when I first start the truck it will rev high 2-3 times then idle around 600 RPM with no more high revs.
- Dan M
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Kendall
Dodge Dakota
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5/27/2008
21:47:07
| RE: reving idle when cold
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Idle air valve dirty or sticking.
Idle air valve is on the throttle body.
Carefully clean the innards.
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LOL
Dodge Dakota
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5/28/2008
10:58:37
| RE: reving idle when cold
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Carefully clean the "innards"
kinda like cleanin catfish eh ???
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Kendall
Dodge Dakota
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5/28/2008
19:18:53
| RE: reving idle when cold
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Sorta, only the guts gotta go back in when you're done.
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Dan M
Dodge Dakota
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6/03/2008
09:55:56
| RE: reving idle when cold
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new MAP and new IAC, still revs high when cold. First rev will be high (1200 rpm now) but not as high as previously, second a little lower (1000), 3rd lower still. Done within 5 revs now.
Overall the truck now runs much smoother.
- Dan M
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SDave
Dodge Dakota
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6/03/2008
10:28:07
| RE: reving idle when cold
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It sounds to me like the coolant temperature sensor is bad. The fact that you say that it doesn't do this after the truck warms up and goes into closed loop indicates this to me as the problem.
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jayb
Dodge Dakota
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6/03/2008
21:14:20
| RE: reving idle when cold
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maybe theres a cat down there hitting the gas....
probably the coolant temp sensor. after that i dunno.
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Greg
Dodge Dakota
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6/12/2008
21:25:56
| RE: reving idle when cold
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Mine just started doing this as well....it revs, then slows down, revs, then slows down. It does it not soon after start up....doesn't matter if it's at operating temp or not.
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Dan M
Dodge Dakota
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6/16/2008
06:45:10
| RE: reving idle when cold
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one other things, seems to only do it in park and not drive. I haven't swapped the coolant temp yet. But I will. I'm around 90k miles so i figured I would just flush coolant, changes hoses and swap coolant temp sensor at the same time.
I seem to remember a post from Larry saying that it was a good idea to swap sensors around 100k miles to keep optimum performance.
- Dan M
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SDave
Dodge Dakota
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6/16/2008
10:23:04
| RE: reving idle when cold
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Greg, if you notice this when you are going at very slow speeds, accelerating from a stop, or coming to a stop then I would say it is the oxygen sensor. You can take it out and clean it with some carb cleaner. Sometimes they can become contaminated and you can clean them and they are fine. If it has gone bad it will become contaminated again, the problems will continue, and have to be replaced.
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pete
Dodge Dakota
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6/16/2008
21:43:19
|  RE: reving idle when cold
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Hey Dan where did you get that $30 MAP sensor from ? my freinds 02/4.7L did this was stumped and through my scan tool didn't throw any codes. Can you run a spreadsheet? with those 2 sensors and see whats going on there I know sounds stupid but could eliminate what could be going on. Maybe that pesky IAC motor hanging up also might want check the voltage on that see how much it varies there only other thing comes to mind watch your coolant sensor temp see how fast or slow it comes up these are some my thoughts to look at take it or leave it
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Dan M
Dodge Dakota
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6/28/2008
18:50:10
| RE: reving idle when cold
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Looks like my reving idle when cold problem may be solved.
I finally got around to checking/changing the spark plugs in my truck. I decided to play it safe and disconnect the negative battery cable. When I was disconnecting it, I noticed when i was pulling up on it my entire negative battery post was coming out. I don't mean the terminal on the wire, i mean the entire negative post was coming out of the battery!
I took the battery in and bought a new one. I finished swapping out my spark plugs and installed the new battery. When I cranked it up, no reving idle!
The plugs I pulled out were the halos. All were a nice brown tanish color. the only thing i noticed was the the #1 plug (driver side closest to fender) had a little brown residue on the ceramic piece itself close to where the screw portion of the plug is.
I installed E3 plugs.
Pete - I think I bought it at autozone. my first choice is always advance but I don't think they had a listing for MAP sensor. actually, I think i bought the map and iac both from autozone.
- Dan M
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Dan M
Dodge Dakota
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6/30/2008
08:10:50
| RE: reving idle when cold
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after sitting over night (it's been 80+ here during day) when I started the truck up, it did rev again. It only does it in neutral and open loop.
next step - swap coolant temp sensor.
- Dan M
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