I rebuilt the original 5.9L magnum and 46RH tranny in a 1995 Ram 2500. That is not the issue. Before the rebuild the issue existed and after the rebuild the issue still exists.
Information: The truck fires up immediately and runs. The tranny shifts and runs as should (as best as I could test it on the road with existing issue). The IAC is not functioning proper - huge sucking noise at idle. The truck has a consistent afterfire (exhaust pipe is making a loud bang). When I turn the throttle under the hood it will stumble and the afterfire gets worse. With consistent air coming in the flaps (opposed to the IAC channel) the ECU/PCM will adjust and it runs great from 1500rpm to 3400rpm. At 3500 rpm there is a stumble and the engine will loose rpm (about 250-400rmp) and slowly start loosing a consistent rpm. The idle circuit whether in closed or open loop operates that same, IAC circuit sucking and after fire, low idle, will die from low rpm, inconsistent accelerations and if you punch it (WOT) it does not respond most of the time.
What have I diagnosed...everything except for using a digital oscope.
My question and needing help...I do not have a digital oscope (only analog). The parts cannon will not solve this problem and IMO it can only be located with a digital oscope. Should be get a $400-500 picoscope or how would I find someone qualified to work on? Someone that actually understands the electronics without OBD2 and scanner information. I live in the Kansas City, MO area and basically, looking for someone qualified to get paid to diagnose, someone in the area that can assist with a digital oscope, or just buy a cheap picoscope.

 

There are software driven scopes out there now.... 2-300 bucks. Just need a laptop.

Test the sensors that you can, TPS is a big one. Looking at the data while the engine is running can also be enlightening. One bad sensor can make the engine run like... well, you know.

 

I would be happy to spend 2-300 bucks for software oscope. From what I know the issue i have seen with that - I can only check the hall circuit with 5v. Unfortunately, the 1995 has an 8v hall circuit also that runs around 9v. So, I dont know if the software/5v laptop D-Oscope would work. But, if you know of something that I don't I am reading! And yes, I have checked all the sensors as far as the multimeter and analog can. I honestly think there is a bad wire/connector somewhere and that is going to be a tough find with continuity and voltage drop.

 

When my 96 was exhibiting that kind of behavior, it was a combination of problems. Cleaning the IAC, and putting a known good IAC (mopar only please), solve some of my problems, replacing the crank sensor fixed the rest..... Now, the 96 is kinda/sorta/almost OBDII..... so, I would get the flashing checking engine light when things started getting really wonky at large throttle openings..... I don't recall if the OBDI does that trick or not. (it's been a while..... )

 

Can you find a scan tool that can talk to the old OBD1 PCM ? That might yield some clues. Don't remember the emissions setup on the older 2500s but the sucking noise could also be a stuck vent valve or EGR os something along those lines. Also, did you check fuel pressure ? Sounds like you're having lean pops.

As for the scope, I assume you're looking for something that can store waveforms otherwise an old analog scope would do the trick. There are cheaper alternatives both PC based or handheld but it requires some research if they are any good. The Picoscope stuff is sort of the industry standard.

 

As far as I know the only scan tool that will work is the DRB3 which is long long gone and are very rare now days. There are compatible scan tools out there that only read a code (one can manually get the codes with ignition on/off procedure). The sucking noise is not the EGR, I have closed off the entire vaccum system other than port vacuum, which includes the EGR system and had the same results. (Good idea though, thanks for the input) I did have low fuel pressure on the rail (22psi) and I replaced the fuel pump and have good consistent fuel pressure with no leaks showing on leak down test. There is for sure lean pops from too much air and I assume the FI pulses are too long because of the MAP reading. However, this is the problem I am having I cannot capture the MAP, FI pulse because I don't have the capability to record It could be a bad wire somewhere but, I am shooting arrows in the dark without waveforms. I found a couple of inexpensive oscopes that I might have to breakdown and buy ($250) that have 2 channel.

 

Snap-On MT2500 does pretty good on OBDI, they are still available too. (MTG2500 also does graphing..... which can be helpful as well.) With the right cartridges/keys, they will work on vehicles up to 2006, I think.

Sucking sound is likely from the IAC. Air flow thru a small hole can get loud. Usually indicates a dirty throttle body though...

Have you reset the computer after changing various parts?

 

It is 100% the IAC and IAC bypass hole in the throttle body. It is clean, I have tried known good IAC (the actual part, I have a couple of 2nd gen rams, i have swapped parts to check if operational). I have tried the disconnect the battery, turn the ignition on for 30 seconds (that is the only way I know), same results. I read somewhere about an IAC calibration/reset but I have never heard of that. It might be that simple if that actually exists. I did read about the MTG2500 and that might be an option (going to keep researching it).

 

There isn't really a 'reset procedure', per se..... What I do is, disconnect battery, turn on headlights, turn off headlights, reconnect battery, turn ignition to on, count to 10, (don't touch anything) THEN start the engine. PCM usually figgers out idle fairly quickly. If it doesn't, there is something else going on.

 

I will try that step by step reset. Then post results.