I have a 98 dodge ram with the 5.9 liter engine. I have a code P0505 for the idle air control system. Truck idles at about 1500 RPM and you can hear a sucking noise from the trottle body where the IAC goes in.

I have changed the IAC motor with 2 different brands and still not working. I have checked for vacuum leaks and none found, inspected wires going to the iac motor and all looks good. I tried hooking up the old iac motor (not installed) to see if it was working but when I turned ignition on i got nothing, no movement from the iac pintle.

Can anyone please help me with this....

 

Did you disconnect the battery after you replaced the IAC? After replacing the iac you have to pull the battery in order to reset the pcm and for it to relearn the everything. The other option you could try is using a can of carb cleaner and cleaning the iac port and around the throttle plate.

 

get an IAC from the dealership they are the best.

 

I have pulled the TB and clean with carb cleaner including the iac port. I did pulled the neg terminal from battery and turned lights on to reset pcm. The iac motor is not moving at all when key is turned on. I have watched it at top of throttle body with flash light and I tried to take the old iac motor and plug connector to it and turned on key and again no movement from iac. Does anyone know witch ports on the iac connector should have power.

 

Grab the 01 service manual from the faq section here, it wil have wiring diagrams, and some simple troubleshooting for IAC issues.

What we really need, is someone to upload the diagnostic manual.......

 

some of this i know to be true, other parts i'm just guessing, so beware.
i've fought it out with the IAC a couple of times.

as you probably already know, no air can pass the closed throttle plate, so the IAC is critical to maintain idle when your foot is off the gas. with the throttle closed, and the IAC closed, you have no idle. with the IAC wide open - you get the 1500+ rpm idle. you can prove this by removing the IAC and using your finger as a substitute.

so your problem is a wide open, or mostly wide open, IAC that won't close down.
(other problems can be no idle, or surging idle)

make sure you have no obstruction that prevents the pintle from closing down.

i'll get flamed for this one.. but, another test is to remove the air filter so you can see, then remove the IAC, and apply some strategic duct tape over the IAC ports to create an idle speed. then with the IAC connected, add/remove duct tape to increase/decrease idle speed and watch the IAC for movement (as it tries to open or close to maintain correct idle). if no movement occurs, then either the motor is bad, or there is no voltage signal to the motor, or there is some kind of bad crank sensor circuit not sensing the idle speed, or some bad mojo in the PCM.

since you've now tried 3 different IAC's, that proves it not the IAC itself, but some kind of failure in the IAC circuit.

so pay attention to the code P0505 - IAC SYSTEM Malfunction. google how to test the IAC system, and what to probe, and when to test continuity of the iac motor, and when/where to test for voltage (12 or 5 or other). consider that you might have a short putting 12 volts where there should be 5 or none. also consider a 5 volt short to ground.

like hey said... a diagnostic manual would be nice.


just a oh-by the way, that probably has nothing to do with your problem. after replacing 3 or 4 IAC's and not fixing my surging idle problem, i blindly replaced the tps and it fixed it. i don't know why, but it did. some kind of funny interaction that i'll probably never understand. i had no codes. you do - so always follow the code...
http://www.obd-codes.com/p0505

 

FIXED.....replaced engine computer

 

I too have done 2 different IACs and a TPS to no avail!! I was afraid I would have to replace the ECM but it is starting to look like that is the only fix.

 

yeah, the drivers for the IAC fail, and that's what you end up with. New PCM is only fix.