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Ask Dodgerench Your Own Question
Dodgerench, ASE Certified Technician
Category: Dodge
Satisfied Customers: 3407
Experience:  30+ years Dodge/Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
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My 98 dodge dakota, with a 3.9L V6 will stall when in idle ...

Customer Question

My 98 dodge dakota, with a 3.9L V6 will stall when in idle or when I let off of the gas while driving. I replaced my idle air valve and it has not fixed the problem. It seems to do it more often if only when the weather is cool and there is alot of moisture in the air. Do you have any idea why or what is the problem?
Submitted: 9 years ago.
Category: Dodge
Expert:  Dodgerench replied 9 years ago.

HiCustomer welcome to Just Answer!.

You should be in good shape. With a fresh idle air control (IAC) motor and no CHECK ENGINE lamp problems, this will probably work out to being just a throttle body cleaning, needing a new battery or both.

Dirt buildup in the throttle body bore and blade margins cuts off what is called the throttle body minimum airflow... a metered air leak built into the throttle body. Without this airflow, engine idle becomes more dependent upon the automatic idle system and small mistakes can cause stalling like what you're seeing. Moist air tends to be slightly lower in 02 because of the water displacement and the quenching qualities of the water, making it quite likely to show up more during those times. Defroster use will add electrical and mechanical loads to the engine when the A/C compressor is activated as well.

Remove the air cleaner above the throttle body and inspect the margins between the t-body bore and blades for deposits. This is the area that passes closed-throttle airflow and it's where you'll be concentrating your efforts.

You'll need some throttle body or carburetor spray cleaner and a toothbrush or a shop rag. Spray the dirty areas down and then open the throttle blades so you can get the brush or shop rag inside. Clean as best you can and then rinse the area down a bit to inspect for residual dirt in the bore at the place where the throttle blades shut. It sticks pretty well, sometimes taking three attempts to get it clean.

Starting the engine will be a little slow with the cleaner that's gotten into the air intake system, but can be speeded by using throttle... clear up to wide open if needed. Once idling, give the dirty areas that couldn't be reached by hand a shot with the cleaner. Engine vacuum will draw the cleaner through the opening and clean the tighter areas to complete the procedure.

If your battery seems a bit weak, it may be a contributor to the idle problem. It might seem odd, but what happens is that the IAC motor step count is lost by the engine controller (PCM) when system voltage drops too low while you're cranking the engine.

The IAC is controlled in pulses or steps by the PCM, allowing it to "count" the number of steps in or out that it's travelled. There is no direct feedback to confirm whether the IAC was actually able to complete these commands, so if low system voltage prevents the IAC from reacting fast enough to complete the step, an accurate count is lost. This can happen incrementally or all at once, depending upon how low the system voltage drops. I like to see at least 10.5 volts during engine cranking, more is preferred. A great many of my customers are surprised when an actual voltage test is performed and they see voltage drop below 10v...

If you have a bad battery or not, now is the time to do a battery disconnect to reset the IAC step count. Pull either battery cable off and wait 30 seconds, then reconnect.

But don't start it just yet. Roll the key on, count five, then crank the engine. The relearn happens right after memory has been erased within the first few seconds of key-on time. If the PCM is forced to try to support an idle before it learns the step count properly you won't be any better off.

From here, you should be good. If the battery is weak, it's time to recycle it.

Write back if you have any questions.