So I am most of the way thru a rebuild of my 1996 Dodge ram 1500 5.2 4x4. Complete engine rebuild, transmission rebuild, suspension, brakes, everything. Was taken all the way down to frame rails. She is 99% back together but have an issue I haven't been able to solve. It acts like the idle control valve is not working. Once warm it has all the typical symptoms, idea drops turning wheel putting extra load on engine, reviving engine results in idle dropping and recovering. ect. Have now tried original IAC valve, and two new ones. All same result. Using USB inspection camera I have watched the IAC valve moving in and out so it is confirmed working. I have also used inspection camera to confirm plenum is dry and shows no signs of oil leaking. Retested engine compression and it is fine. Problem is soon as it comes off high idle problem shows up. Gut tells me it has to be an electrical/sensor issue but don't want to just randomly toss parts at it. So what are other good candidates? Or any good suggestions for reading engine parameters to confirm? Like I said truck was completely taken down to frame rails so just about anything is possible. So what acts like IAC valve or plenum but isn't?

Thanks, this is one of last issues I want to figure out before I finish putting it back together and getting it back on road......

 

Random vacuum leak. Try blocking off vacuum ports on the intake and/or spray something flammable like brake or carb cleaner along the intake/head area.

 

There are a lot of vacuum lines in front of the passenger side connected to the side of the intake and there is a check valve that looks like the once in the picture below. Atleast in my truck. Make sure that its facing the right way i had similar symptoms when mine failed.

 

Both good suggestions, but no progress. Double checked that check valve and it is functional and installed correctly. I also used half a can of brake cleaner and couldn't find any vacuum leaks. Actually if I do induce a vacuum leak idle goes up and problem seems slightly better as more air is being introduced into engine bypassing IAC valve. In my mind it is like the IAC valve isn't openning far enough or fast enough, but I again confirmed with inspection camera that the IAC is moving in and out to try and control idle. So what could cause IAC to not adjust enough? or what other sensor does engine controller use to determine how much IAC needs to open? Any type of calibration?

 

Is that a mopar IAC valve in there? If not, think I would be looking for one.....

 

did you do the engine fuel sync w/ a computer. this might also affect idle if the distributor isn't set perfect. It's the only way to properly time it. I had similiar issue w/ my recent 5.9 rebuild, hooked my computer up, turned dizzy about 1/8 inch to get perfect fuel sync and idle problem went away.

 

Standard Motor, Had good luck with that brand, but I have considered this. Think it is more likely I have bad wire connection either to this sensor, or another sensor. Trying yet another IAC is on my list, but think it has a low probability of fixing it.

 

Not sure what exactly you are suggesting. details? Really can't see how it would be timing issue, but listening....

 

If you removed the dizzy set the fuel sync! Engine needs to be on #1 TDC ON THE COMPRESSION STROKE. The dizzy should look like this...

 

Yep, this was done with engine on stand when the distributor installed. I haven't 'fine tunned' it with scan tool. or reading came position sensor. Probably a worth while exercise, but not sure it is the cause of this issue. I should be close enough. Still I will be looking at this. Don't think any of my scan tools will do this, but could probably set by back probing the cam position sensor wire. Truck isn't on road yet so taking to dealer isn't option (still no lights, or bumpers installed and I want to get this straightened out before I button everything up)

All that said, problem doesn't seem to be a fuel related issue, seems to be air and I suspect IAC isn't opening up enough or some other sensor isn't give it correct data causing the under corrected opening..