IAC
I had changed my IAC back in 19 or 20, for P0505, to no change, after severe TSing by the book.
Still having idle problems and code - code was instant with key-on w/ or w/o start.
I had ordered a BorgWarner, they sent a Standard - so 'free'.
So, TS again.
Found a bit of resistance between the inner set of wires, that went away with C1 disconnected from PCM.
Did that for 1/2 hour, then realized water was moving in the plug C1.
Lost an hour dis- and assembling that (open and hair dryer next time, DO NOT DISassemble).
(Also, double blue **** release all the pins, do not disturb, locked when double 'IN'.)
Anyway, still getting instant code.
Put old IAC back in, code was not instant, but with actual start but great idle control.
Standard in trash, left old OEM in, ordered new real OEM.

Since that was improving...
I decided to charge AC a bit
Charged some, outlet temp went down, but not right.
Remembered I had a hand valve in heater line.
Closed that, started - no IAC light!
Wait - no panel, no bus!
Everything worked except panel, so I went on home - AC better!
Reconnected all the PCM C1,2,3 stuff in case I had leaned on them - no change.
Web said sensor this, 5 volt that, and bang on dash - that worked!
I hate to guess at correlation, but moving the HW valve and NO BUS were strangely coincident - wow!

Dash tapping continues to work, will remove panel and reseat sometime.

 

OK, my new IAC arrived.
When I relearn (battery out for x minutes), do I want the new IAC to have been left (to be 'found):
fully extended in open air, or
fully extended as installed (as far as TB will allow), or
fully retracted.
I can figure out how to force any of these positions, seen all referenced in posts - which is right?
('Give it the finger' will force fully retract as it tries for more air, and 'open other vacuum sources' [brake valve for instance] will force fully extended in place or otherwise as it tries to close off excess air.)

WHICH IS BETTER ?

 

Well, no help?

I gonna guess system spends more time at near closed - as idle is close with device extended out / passage closed / running on butterflys.
So, nearly closed is probably needs a more precise setting.
Nearly closed would be the reaction to the 'installed with extra vacuum open' situation, so I'm gonna' try that first.
(Running, open additional vacuum source, device moves to close port, disconnect wires, all off, disconnect battery x minutes, battery reconnect, key on 10 secs, key off, start!)

Any help out there?
.

 

OK, more clues...
I find that if I disconnect and reconnect C1 at the PCM, 5 key-on's will not cause a code.
(Based on Dodge TS steps, this proves PCM good.)
Standard is in the trash.
My new Mopar IAC will throw a code.
(My old Mopar, uninstalled, will also throw a code.)
My new one, after extra vacuum learn (I assume pintle extended) was revving high (1200 or so).
Then, my new one, after finger plug learn (I assume pintle retracted) was revving high.
(I tried both, because if I left it fully extended or retracted, maybe to couldn't go the other way if a wire/driver was bad?)

Anyone read through my troubles and recall a fix?

 

When I replace an IAC, I also clean the throttle body REALLY well. They tend to get gunked up, so the pintle can't move properly. Leave the battery disconnected while you clean/swap parts. When you have it all back together, turn the ignition to "on", (not start) count to ten, THEN start the engine. (and don't touch anything other than the key.) This gives the PCM a chance to relearn 'zero values' of the various sensors. It should figure out idle fairly quickly.

Do not energize the IAC when it isn't mounted. It will launch the pintle, and then the IAC is toast.

 

I'm 200 miles out from a bottom end, plenum plate, flush, and throttle body work.
So everything is freshly pristine.

 

Try doing the PCM reset procedure anyway. See if idle is more where it should be.

If not, poke around for vacuum leaks.

 

I reset PCM each change.
Starts with high idle and slowly learns it's way down with trips.

 

NO BUS tells me something happened with the 5v rail in the system and when this happens usually the PCM go's not to long after, either you have another sensor that is wigging out like the crank/TPS or your PCM is on the way out. before my PCM blew I had the same symptoms and replaced everything to do with high idle trying to track the problem down but I could never get it fixed until the PCM blew so I got a new PCM and the problem went away.

So you smacked the dash and the nobus error went away? you should check the connections for the gauge cluster if smacking the dash made it go away this could mean the gauge cluster is either not secured properly or faulty which will kill the 5v regulator in the PCM over time. The idle could be wigging out because the 5v rail is fluctuating making the sensors reading fluctuate either due to bad sensor, bad PCM, bad gauge cluster or bad ABS module. Usually with NO bus you want to look at any sensor that uses the 5v rail, ABS module, Dash cluster or the PCM itself... for instance a burnt wire on a 02 sensor that bobs mechanic left on the exhaust pipe can cross the 12v heater wires onto the 5v rail which will fry the PCM and other sensors, it can also cause idle issues before it fully blows so make sure you trace the 5v rail around the vehicle to see if there is a short somewhere. 02 sensors seem to be the biggest problem with NOBUS that ive seen.

if you ever get to a point where the NO BUS is persistent and cant start the vehicle you can try getting a USB phone charger, plug it into the cigarette/power socket in the front then cut and run the the positive from the phone charger to the 5v wire on the TPS, phone chargers use 5v so if you hook this up to the TPS and don't have a NO BUS error anymore that means the 5v regulator is shot and you need a new PCM. you can run the truck like this temporarily but I don't suggest doing it for a long time because back feeding power like this will kill the PCM even more with time its more for testing and moving the vehicle when you need to.

some people have gotten their own standalone 5v regulator and bypassed the PCM so the PCM doesn't blow as this is actually a fairly common problem for these PCMs but I do not suggest this for a variety of reasons, its better to just swoop up a PCM from a junk yard that has the same engine.




PCM compatibility just in case you need a new PCM in the future:

-<2000 if you have a vehicle with security you can grab any PCM from a vehicle with the same engine and it'll work, if the vehicle you got the PCM from didn't have security your vehicle will turn the PCM into a security PCM when you hook it up automatically.

-<2000 if you have a vehicle without security you'll need to find a PCM from a vehicle with the same engine that doesn't have security, if you put a security PCM on a non security vehicle it'll lock up and not let you use it because your vehicle has no way to disarm the security.

-2000>if you have a vehicle with a grey responder chip key you'll more than likely have to get a brand new PCM from dodge and have them program it for you at the dealer if they still have the ability to program these at that dealer. (you'll have to call around because most dodge dealers wont do it anymore sadly)


[edit] also make sure you check all vacuum hoses to make sure you don't have a leak anywhere. my truck has 2 or 3 extra ports on the intake that stay capped so be sure to look around the intake and see if there are any open ports that should be capped or might have wiggled loose.

 

THX for help, after last smack mentioned no further problems.
Seems to be strictly isolated to the dash.
Next time in I will clean connectors!