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Chris H
Unregistered
3/18/2001
11:25:04
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 Subject: High Idle on 3.9 TBI
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Message:
My 93 3.9 idles way to high, 1200 - 1600 RPM cold and warm. I've removed and cleaned the IAM, it had clean lines where it has been seating and I can feel the valve moving ever so slightly with my finger with the engine running. Is there a shade tree method of testing the IAM out of the throttle body or should I be checking some other control? Don't have the budget to buy parts that I'm not convinced are bad. Thanks.
Chris
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Bernd
GenIII
3/18/2001
11:52:10
| RE: High Idle on 3.9 TBI
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Message:
IAM? You mean the IAC (AIS) Solenoid on the back of the Throttle Body? If so, cleaning it means wiping the "gook" off of the plunger. Do not turn it (twist it) otherwise you will damage the solenoid. I believe they're about $50 at most parts stores for the older models.
As for testing them, without a scanner to actually see what the PCM is telling it, no. (It's 5V ON/OFF regulated by the other inputs to the PCM.)
Bernd D. Ratsch
1997 Dodge Dakota SLT
Supercharged w/Nitrous
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87Dakota
Mechanic
3/18/2001
18:07:00
| RE: High Idle on 3.9 TBI
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Message:
First off I would just check out the wiring leading to the solenoid first. (easiest) And test to see how many volts are coming out of the wires. As for testing the solenoid there are special adapters you hook onto it and then connect it too the battery. Not sure where to get them though, their pretty useful if you do a lot of work on cars.
Nick
1987 Dakota 3.9L, 3 speed, 220,000 miles
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Chris H
Unregistered
3/19/2001
00:55:17
| RE: High Idle on 3.9 TBI
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Message:
I stand corrected, IAC.. That's what I get for looking at a Chiltons manual..
Yes, cleaned the gook from it, no twist, bang etc. and no vise grips.
I have access to a basic scanner, not sure if it will exercise the solenoid or not but it should tell me if the PCM is sending signal or not. I was hoping for a home made adapter, can't justify buying one for one use. Thanks!
Chris
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Bernd
GenIII
3/19/2001
09:09:39
| RE: High Idle on 3.9 TBI
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Message:
The IAC is regulated mainly by TPS and O2 inputs via the PCM. You can test the soldenoid to see if the ground is good and to check the 12V/5V input/output. That's about it.
Bernd D. Ratsch
1997 Dodge Dakota SLT
Supercharged w/Nitrous
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chris H
Unregistered
3/20/2001
17:29:45
| RE: High Idle on 3.9 TBI
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Message:
OK folks, had my IAC out of the TB with the engine running (and a clean rag stuffed in the port) and I can feel it pulsating but it doesn't appear to be moving in or out (regulating idle speed by hand). Any thoughts? You think my problem is a bad IAC? Thanks.
Chris
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Bernd
GenIII
3/20/2001
18:40:24
| RE: High Idle on 3.9 TBI
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Message:
It should move a little bit back and forth...but hard to say with what you said. How many miles are on the truck? (If it's over 60-80K, might as well change it out.)
Bernd D. Ratsch
1997 Dodge Dakota SLT
Supercharged w/Nitrous
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chris h
Gen II
3/20/2001
22:55:29
| RE: High Idle on 3.9 TBI
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Message:
147K miles, bought it used with high idle so I think I'll change it. Thanks for all the help.
Chris
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chris h
Gen II
3/21/2001
22:23:17
| RE: High Idle on 3.9 TBI
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Message:
New IAC did the trick. Funny part is the OEM number didn't match my engine. Watch for new post with details.
Chris
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scott
Dodge Dakota
JOIN HERE
8/10/2014
17:47:29
| RE: High Idle on 3.9 TBI
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Message:
My 97 is idling in park at 24/2500 rods when it is in gear it is i
dleing about 300 more then it should and the temperature is
about to soon as you crack it up what could it be
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USA
Dodge Dakota
JOIN HERE
10/08/2014
17:36:49
| RE: High Idle on 3.9 TBI
IP: Logged
Message:
What is happening to this country? The above post is from a high school graduate.
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