IAC technical issue

Hey guys I’m new to this forum, I have an issue that I’ve been chasing for a couple weeks now And am looking for some extra info. So the back story with this rig is I just got done building it and it ran fine and I got a random IAC code, at the time it ran fine but a day later the idle started having issues. I swapped out another T body and it ran fine and code went away for a few day. After a couple days I. Prices when I would start the rig the idle would stay low even when cold. It’s been about 1000 in park and 6-700 in drive. I swapped the IAC again with another and still have the same issue. I can back probe the ecu signal wires and get the idle to go up and down on command. I have 12v at the IAC so that checks out. When checking the other two wires that should be about 6-8v they also have 12v. I know the ecu is supposed to control the two other wires so idle control but I’m getting just constant voltage back through the IAC. I checked at the ecu and the control wires are good and also can back Probe from there And get the idle to work in demand. I opened up the ecu and can’t see anything out of the normal. Could there be another sensor the controls the IAC that I’m missing or does anyone know what I may be missing. Sorry for the long message. Thanks

 

So what do you define as "running fine"? I think my car's RPMs in Park are similar to yours. Not sure in drive, and stopped but usually RPMs go down.

Isn't there a TPS that factors into the idle too?

Vacuum leaks will cause issues too.

So yeah...there are lots of things that affect idle.

 

All vacuum Line are good and i have a p0505 code. Also lost my high worm up idle at start so at start when cold or hot it’s always at about 1000-1100. It should be around 700 when worn. i did test the IAC and swapped it out as well with a spare. I have 12v going to IAC but don’t have the signal voltage from the ecu on the command wires to the IAC.

 

Did you ever find out what the issue was?

I have this EXACT problem. Been fighting it for a year and can’t figure it out.

I just replaced the whole throttle body (came with new IAC and TPS). Also new hoses coming off IAC.

Yet I’m STILL getting a code.


Any help would be appreciated