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Idle problems

Tiny
STARLORD1976
  • MEMBER
  • 1998 DODGE DAKOTA
  • 3.9L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 150,000 MILES
When I start my car the idle it will rev up and down and if I touch gas pedal and let off it will rev up real high by itself. Already changed IAC valve, TPS, and MAP sensor. Cleaned carburetor. Cannot find anything sucking in air. What might be going on here?
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Sunday, January 21st, 2018 AT 7:13 PM

14 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Lets start by running the codes because it sounds like you my have a MAF that is out of range. Here is a guide to help us get started:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Also, lets check the engine for vacuum leaks.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Please let us know what you find. We are interested to see what it is.

Cheers, Ken
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Tuesday, January 23rd, 2018 AT 10:22 AM
Tiny
STARLORD1976
  • MEMBER
  • 173 POSTS
Only code I have is fuel injector circuit open, will that cause it?
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Tuesday, January 23rd, 2018 AT 10:27 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Yes, that will cause it, it sounds like you have a shorted fuel injector. Here is a guide to help you test the injector:

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

Please let us know what happens.

Cheers, Ken

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Wednesday, January 24th, 2018 AT 10:03 AM
Tiny
STARLORD1976
  • MEMBER
  • 173 POSTS
I am sorry, but I read that code wrong, there are no codes showing up.
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Wednesday, April 11th, 2018 AT 5:11 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
I have seen where the distributor timing being off will cause this. If that is okay it sounds like the computer is having a problem but to be sure lets test the engine computer wiring to confirm the failure. Check ground and power wires as well.

https://www.2carpros.com/articles/how-to-check-wiring

Here are the engine wiring diagrams and PCM location. Check out the diagrams (below).

Please let us know what you find. We are interested to see what it is.

Cheers, Ken
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Wednesday, April 11th, 2018 AT 7:06 PM
Tiny
STARLORD1976
  • MEMBER
  • 173 POSTS
I took my truck to the shop and they said they could not find what was causing the idle problem. They said they ran a diagnostic on it and nothing showed up either. If I had a messed up PCM would that show up. Not sure what to do now.
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Monday, April 16th, 2018 AT 8:30 PM
Tiny
KEN L
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Yes, a bad PCM can cause the problem and to find out for sure you must send it to a re-builder to be checked out. I would try a used one plug and play.
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Wednesday, April 18th, 2018 AT 11:30 AM
Tiny
STARLORD1976
  • MEMBER
  • 173 POSTS
I have one more question. I noticed the middle plug that goes to the PCM is not original, it has been added. Is it possible it can be in the plug or plug wires and how can I find out?
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Wednesday, April 18th, 2018 AT 11:39 AM
Tiny
KEN L
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  • 48,363 POSTS
Can you upload a picture of the connector so I can see what you are talking about?
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Wednesday, April 18th, 2018 AT 11:42 AM
Tiny
STARLORD1976
  • MEMBER
  • 173 POSTS
The old connector is cut off and there is a new one wired and taped up in its place.
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Wednesday, April 18th, 2018 AT 11:46 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,576 POSTS
That could cause it if a single strand of wire managed to create a short, if it was on one of the control feeds to the IAC it could cause it to move and not show as a code.
Was the shop using a DRB3 or an aftermarket (Snap-on, OTC, Launch) type scan tool?
Some do not play well with Chrysler's and may miss things the DRB will find.
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Wednesday, April 18th, 2018 AT 2:03 PM
Tiny
STARLORD1976
  • MEMBER
  • 173 POSTS
He just said his big machine is all I know.
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Wednesday, April 18th, 2018 AT 5:04 PM
Tiny
KEN L
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I would go back to checking the wiring pin to pin and then to ground. Make sure the wiring is in good shape and that none of the strands are touching. Refer to the post above.
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Thursday, April 19th, 2018 AT 10:01 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,576 POSTS
Like Ken says, go over the place where the wiring was spliced. It is possible that the connector was off a different model as well and they just matched color for color. The catch to that would be if there is a pin that was different between the two.
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Thursday, April 19th, 2018 AT 11:11 AM

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