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1994 Dodge Caravan 3.3L
Understand IAC is a stepper motor and PCM controls steps in and out. Believe steps range from 0 To 200.
What I don't understand is this:

1) Does the PCM keep a "permanent" IAC count (last step count at shut-down)
OR
2) Does the PCM reset the step count (say back to zero) at Start-Up or Shut Down and retract the Pintel to that base position ?
3) At "Initial" Start (KEY-ON) where should IAC pintel be located?


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contributions: 2089
Images: 37
Location: Oregon
the iac position is relative to where the computer wants your idle to be at. The iac is just an opening between the front of the throttle plate and the back of the throttle plate. The pcm want your idle to be at a certain rpm and adjusts the iac so that the engine achieves that rpm. If there are loads on the engine, like from park to drive, the ac turns on, you turn the headlights on, the defroster on, all those things will pull the idle down so the iac will bring the idle back up to keep it at what the computer is programmed to see from manufacturer.

As time goes by you can develop coking on the throttle body that will reduce the amount of air that gets by the throttle plate. The Iac will compensate for that loss of air flow. So the iac counts will go up higher. If your iac count is zero you should still have an idle of 575 t0 875rpm. (minimum airflow) Depending on how cold your engine is and the loads on your engine the actual iac count will vary. Even a very dirty air filter can affect your iac count.

are you having a problem with your vehicle? It would be helpful for me if you would tell me why you are looking for this type of information.


   
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Thanks for responding. Pic looks like (around) 1966 charger. Friend had one back then. Had a 1974 myself.

Yes. Been working on an intermittent No-Start / Stalling Issue for almost a year.
See this link: http://forum.chryslerminivan.net/showth ... 0085aad3b7
Last post today (#55).

FWIW: Not much of a part changer. Only have 98600 (deceased father orignal owner) on vehicle but because of age and year long issue redid fuel system
(Tank, Fuel Module, Filter, Regulator, Hoses) about two weeks ago. Didn't solve the intermittent and raised some new questions such as:
What is an acceptable leak down rate?. For example, No leakage at injectors IMO -- but a pressure drop
from spec (48 psi) to 5 psi in a five hour period.

Is this normal (acceptable) and if NOT, what is normal?
Chrysler shop also says two check valves inside module (supply and return). Why on the return side?


   
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contributions: 2089
Images: 37
Location: Oregon
Read your 6 pages. you need to start with the basics. forget everything and keep some equipment in your vehicle so you can check it when it dies and won't restart. You need to check for spark, injector pulse and fuel pressure, when cranking. Find out if one of those things are not working. If you have a code reader or scanner, check your coolant temp and your fuel trims.

If the IAC was the problem you would be able to start the vehicle by opening the throttle by the gas pedal and bypass the iac so I don't think that would be your problem. The Iac could be a problem if it stalls when you come to a stop because of throttle body coking but it should still start up afterward. (do a minimum idle test to check for coking)

It could be possible that you have more than just one problem.


   
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Quote:
start with the basics. forget everything


Agree (Aiir, Fuel, Spark, Compression).
Fuel is easy, can run around again with a Fuel / Pressure guage taped to window..
Spark another issue. Have thought of getting some extra long plug wires and inline spark tester and also taping to window.
Once it dies, no better than where I'm at.
Use a stethoscope and in-line LED for injector pulse.
Scan tool worthless, no codes.

Right NOW, see post #56, few minutes ago, this car is dead in the garage.

Quote:
If the IAC was the problem you would be able to start the vehicle by opening the throttle by the gas pedal and bypass the iac so I don't think that would be your problem. The Iac could be a problem if it stalls when you come to a stop because of throttle body coking but it should still start up afterward. (do a minimum idle test to check for coking)

Did try you pedal to the metal to try and start. Got a pop -- not sure what.
After than checked TB inlet. Interestingly the "back side" of the flapper and an oily residue.
Cleaned it an TB area I could reach with gas, so clean now.

Quote:
It could be possible that you have more than just one problem.


Agree

BTW have been using the forum link I gave you to try and keep things in one place for record purposes.


   
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Location: Oregon
Scanner is not usless. but a code reader would be. A scanner will be able to see the data stream while you are driving. you can see the fuel trims, you could see if the O2 sensor goes lean just before it dies. You can see if the computer raises the injector pulse to try and give it more fuel as it goes lean. You can look at the voltage and see if voltage jumps or drops. There are a lot of things a scanner can tell you if you can graph the data stream and then freeze it when the it acts up to see what changed all of a sudden when it died. You can zoom in and see what happened just before the rpm dropped off.


   
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A scanner will work on an OBD-1?


   
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Location: Oregon
Yes, it will


   
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