Hi all,


I have a 1992 B350 with the 5.2L. I just replaced the PCM because the voltage regulator component of it failed. I bought a PCM from O'Reilly's and replaced it.


I proceed to drive the van a few blocks and am now getting a high idle/rev. The motor revs up and down. So I pulled codes and got Code 25 IAC Circuit Short. So I replaced the IAC Control Motor with a MasterPro #2IAC34, which did not fix the issue.


Now I am scratching my head to see what I should check next....should I have replaced the IAC with a CEL Code 25? or should I have done a something differently?


This vehicle is the van for my wifes daycare business I and have to be sure that the kids are safe riding in it....can't have a runaway van loaded with kids...any help would be appreciated.

 

A short circuit indicates one of the wires going to the IAC valve is touching ground or the 2 wires are touching each other. A quick way to check this is to disconnect the IAC and see if you get a different code. If you still get the code 25 then start looking for a short in the IAC wiring.

 

Hi alloro,


I remember you helping me years ago under the handle "wifesdaycarevan". Couldn't remember my password or the email I used so had to log in via Facebook. Anyhow,


I did the test that you suggested and I am still getting code 25. I am wondering if when I replaced the PCM (Oreilly's unit) 79-5141.


The van always ran fine prior to the voltage regulator dying (which required changing the PCM).


If the IAC circuit is the actual culprit, is there a way to test the line with a multi-tester for some valves that might let me know that the wire is shorted?


I pulled the sheathing down the wires (there are 4 of them in the sheath) and I couldn't see any chaffing or wires melted together either. Where can I test the other end of these wires coming from the IAC. Would that be at the main plug going into the PCM. Do you know what pins they might be?


Sorry for all the questions, but I need to get this figured out so I can get wife and daycare kids back on the road.


Thank you.

 

Hi Alloro,


I did the test as you suggested. Still getting code 25. Do you think it could be a bad PCM (I installed a Oreilly Cardone #79-7141)?


If it is the IAC circuit, do you know which pins I should check in the PCM plug that match those 4 wires at the IAC connection. Would checking for continuity be the next step?


Sorry for all the questions, just really need to get this van back on the road. It has provided 15 years of no problems till now.


Thanks for all the help

 

A bad PCM is always a possibility, but as of now all you've done is confirm it's not a bad IAC valve. The IAC wiring has to be inspected all the way back.

 

Ok I stripped the wiring sheathing off down to the next loom (where it meets the injector loom) and cannot see any chaffing or bare wires. Is there a way to test on each end (the 4 IAC wires and the plug that goes into the PCM)?


By chance would you know what pins to check in the PCM plug to look for continuity of the IAC lines? Is it even appropriate to check for continuity?

Also I never get a check engine light. I just do the key dance to see that code 25 is reporting. I have unhooked the battery to reset codes and still get code 25 on a fresh start up.


Thanks for all your help.