Well I don't have the OEM Ford iac that was still on the used throttle body I had. I think I threw it out because it was so rusty. I think it came from up North. I did have a Standard Ignition one that was still on my original throttle body that I swapped back. Although I didn't hook it back up to Forscan it didn't seem to make a lick of difference. I've used countless Dorman products and haven't had any problems out of them. Used many Dorman parts on my Dakota R/T. I would've preferred a Motorcraft crank sensor but I had a new Dorman sensor that I had for months that I never got to putting on. I can see why too. It was a fair amount of work. The whole alternator bracket and coils had to come off. The plastic water pump tube was a pain to get back in for sure. However, I doubt it's giving trouble because it made no difference in the way the engine acted. I gave a tug on all tps, idle air, and egr pressor sensor connectors tonight after I reinstalled the Standard Ignition IAC valve but they didn't change the way it runs. I repaired all the broken connectors a couple weeks ago. I've been watching a lot of Ranger youtube videos and I was amazed to see how many 2.5 Rangers had blown head gaskets although a far cry less than the 3.0 Rangers. One guy had a miss a lot worse than mine. Mine is hardly noticeable until it starts but he had replaced everything I had but still had a bad miss. It turned out his head gasket was blown between 2 and 3. But mine has never once run hot. Even the original motor that died at 228,000 in the 5 degree Kentucky winter while on vacation never over heated even once. Do the head gaskets just blow even without any overheating? But my compression was good. Is there another way just to make sure that the CKP is working right? Can't I hook up a timing light? Is it only suppose to be at 10 degrees while idling or should it move around? What other test can be done to determine if a valve is burnt, bent, or bad? Is the leak down test the only one?

 

Did you ever drive it with the ELM plugged in & a fuel pressure gauge connected & taped to the windshield so you can monitor fuel pressure while driving & it's acting out?

 

The truck hasn't quit running while driving since the last time I responded. I drove all day with the ELM plugged in and I even updated the software to the newest version. I didn't see any abnormal readings except out of the Idle Air valve % was always higher and sometimes lower than Ford's chart but for the most part way higher. I of course have been driving pretty much nonstop this summer with the a/c on. And it works great. I just did an accumulator, hd orifice tube, re-oil, and reseal on the a/c system like last year. I did notice that right after the hiccup/miss or whatever it actually is happens at a long stoplight with the a/c on when it engages that the fuel trims jumped up briefly but not right when you feel the noticeable chug it was a second or two after it. But for the most part even the fuel trims were always well within range of Ford's chart for the 98 2.5 automatic. I had planned on taking it to a trusted shop that I get all my exhaust work done who also does emission testing and diagnostic. I told him the problem and what I've done. He basically said not to waste my time by bringing it to him because I've done just about everything that can be done. And without a Check Engine Light or any stored codes it would be hard to track down. He recommended by what I was describing to him that I should replace the fuel pump. I'm not able to hook up my tester and drive it too fast or on the open road because it doesn't reach far enough back to really see it. It will also interfere with the hood closing which is already lightweight fiberglass. I don't want to be cruising at 45-50 MPH with the flimsy hood partially closed. But I'm getting 65 PSI or a hair under it with it running, with just the key on, or running and in gear. I did move it around the driveway with it hooked up and it stays around there. The funny thing is if you look up the Airtex 2207S it states the minimum PSI for their pump is 85 PSI. Delphi was the only one Rockauto offered that had an operating pressure of 65 PSI, Carter's max pressure was only at 45 PSI and Spectra's at 80 PSI. This Airtex was never 85 PSI even right after we put it in. And the factory specs are only 65 +/- 8. I've tested the pressure numerous times and it's always at or around this 65 PSI range. On the original pump I think the most I had was like 72 PSI. I kept the original pump but I believe I had the pump motor replaced a couple times on it too, so it's no longer original. So is 65 PSI too low? Should I replace the pump? It is under warranty but I have to do a pay and swap out.

 

Fuel pressureSpec on the 98 & up is 64 +/-8 psi, so the fuel pressure number you've measured & posted is ok.
Seeing as how it only does this when the A/C is on & at idle, imo the cut out symptoms don't point to a fuel pressure, or fuel pump problem, or it would do it all the time.

Are the A/C system pressures staying in spec when at idle & it's hot outside? If they're spiking, maybe the cooling fan isn't doing it's thing at idle, to pull enough air through the condenser, or maybe the fan clutch is gong or the fan clutch fluid has leaked & causing it to act out & not pulling enough air through the system?

Are you seeing any coolant temp spike at idle, in hot weather, with the A/C on?

 

I haven't checked the a/c system pressure because I don't suspect a problem. It's not cycling quickly. The interior temp gets to 40 degrees and the accumulator has plenty of condensation on it. Not related but amazingly somehow the passenger floor pan doesn't get water under the carpet anymore. I fixed a door seal that had started to lift a little but didn't think it was the problem. However, the power is getting way worse especially with a drag such as the a/c on. I was able to drive it without the a/c on at all last night because it was cool. It still has a tremendous power loss even without the a/c on. It's not right. I don't hear the miss any longer that was encountered before I replaced all the ignition components. I was still curious so I rechecked the fuel pressure after driving all day in rush hour traffic. The fuel pressure is now on the margin. The pressure tester needle fluctuates extremely rapidly between 56-60 PSI. That's right on the margin. A few weeks ago it was at 65 PSI and have noticed an even more dramatic power loss. It hasn't cut off anymore but it seems like it wants to. You really have to abuse the gas pedal with the a/c on to get it to really take off. I changed the fuel filter back when I was doing the ignition components as part of a basic tune up. What does it mean when the pressure tester needle is fluctuating extremely rapidly? It looked more like between 58-60 PSI but it was moving so fast I couldn't tell for sure where it bottomed out. Also when I shut it off the pressure was down to almost 0 in less than a minute. I don't know if that means anything.

 

That quick pressure drop after shut down & the rapid fuel pressure needle shake are good clues.
A number of things come to mind to put on the suspect list.

Check the fuel rail mounted fuel pressure pulse damper for a diaphragm vacuum leak, by disconnecting its vacuum line to see if it's wet inside with fuel.
Fuel pump drain back valve, or pressure regulator acting out.
Runny nose fuel injector.
EDIT: Do you have any fuel trim trouble codes, or does your scan tool detect any fuel trim anomalies?

 

I've never replaced the fuel pulse damper. I drove last week 100 miles with the Forscan hooked up and the fuel trim were 99% of the time within specs. There was one brief second after the idle chug at a long stoplight the longtrm went a little above specs. But that was it. They were mostly all the time within specs. Long and short trim. I did replace the fuel injectors with a matched set of Motorcraft injectors which were Bosch after we did the ignition system tune up.

 

Well seeing as how the fuel injectors have been replaced, they belong lower down on, but not off the suspect list.
Easy to check the damper to see if it's diaphragm is leaking fuel into it's vacuum line, just disconnect the vacuum line for a look see & sniff for strong fuel smell.
If all that checks out, then that leaves you looking at a fuel pump/pressure regulator, or drain back valve problem, in any case the fuel pump assy.

 

I took off the fuel damper vacuum line. I smelled a trace of fuel vapor but not wet or not really strong. You had to really hold it close to your nose to smell the fuel. I have the fuel pump under warranty. It's about 2 years old. I bought the whole assembly. I bought the airtex because I couldn't afford the $400 Motorcraft. Now it's not even offered but I'm sure it will be out of my price range so I will have to go with the warranty unit. I do still have my original sending unit that's had the fuel pump motor replaced a few times. It's been sitting in the airtex box in the garage since we replaced the assembly. But I think the regulator may have been going bad on it. I don't know how to check it now that it's been out of the truck for awhile. If were ok I could swap the fuel pump motor and see how it works. Luckily it only takes us about an hour to change the fuel pump as we remove the bed. Is there a way to check a fuel pressure regulator that's on the pump and out of the tank? I don't see a replaceable fuel pressure regulator you can buy to change.

 

I don't remember more than one pressure damper being found bad, so it's not a common problem part.
I've heard of folks replacing the fuel pump motor but not the regulator assy, don't know that the regulator assy can be bought separately.

If you can get the fuel pump assy replaced under warranty, seems like that would be the way to go, as it would cover replacement of all three common problem part suspects, the motor, regulator & drain back valve.

Trying to rig a high psi fuel pressure test rig sounds too risky to me. Probably could be done, but one would have to be really careful doing it, so no warranty expressed, or implied!!!! lol

 

If you replace the fuel pump assy, start the engine to check the fuel pump, fuel pressure & pump delivery rate over time, Before reinstalling the bed. Delivery rate should be like 1/2pt/15 seconds of pump run time.

 

I had all of these same symptoms, and followed these same procedures for about the last 2 years on a Dodge Neon. Everytime I thought it got fixed, the problem would pop up again later. There was absolutely no replication that I could do to get it to act up, it was whenever, however, wherever. Obviously, everything pointed to the ignition. I replaced the plugs, wires, COIL pack with a ValueCraft from Autozone and bought a new battery.. I reset the computer after each procedure. It would run better for a few days or weeks, then back to idling down at random. I paid attention to cold start conditions including humidity, ambient air, fuel level, anything. Nothing could replicate consistantly. I then started getting O2 codes, replaced the sensors. Camshaft position code, replaced. I read on the internet that being off 1/2 tooth could cause low idle and engine stall with a/c on. This is an all day job on a Neon but I pulled it apart again to double check, in 2 years I have done it 5 times. I have cleaned the throttle body, replaced the map sensor, replaced the crank sensor after I kept getting a PO339. I have replaced the fuel regulator/pump, all 4 injectors/connectors, cleaned the rail. I went through the whole cooling system, replaced the radiator, hoses, thermostat, temp sensor, cap. The original IAVC had been cleaned early on, then finally replaced. I even replaced the COIL again about a year ago with a DuraLast from Autozone, with no affect.
Everytime I did something, it seemed to get better for awhile. I could use my a/c and no stalling when decelerating or idling, no hesitation on accelerating!
Then, out of nowhere it would idle like heck again. And it wasn't constant. It would run great for a short trip to the store, or a 30 minute drive, then it might run like crap after a 29 minute drive and/or a short trip to the store.
The first summer, I figured the a/c compressor must being going out, but at $400, I drove with the windows down.

Anyway, I know that my first problem is that it is a Dodge, so I am not expecting it to ever run well...

So about a month ago, I am reading about my issues, and everything points to the coil pack. I have replaced it twice, that is literally the first thing I did within the first week I bought the car, with no long term change. But I changed everything except the alternator, maybe? So I changed it. Ran great!!! For 2 weeks.

So I am reading on the internet. Resetting the computer makes it go back to factory settings. So everything is running better until the computer gets feedback from the sensors then it relearns and adjusts. I started resetting the ECU when it finally completed a drive cycle, so that my daughter could get to work with the a/C on. I am still reading on the internet but I am horribly deflated. I am at the point that I am deciding that the problem was my 3rd grade teacher. If it weren't for him, I am pretty sure my car would be running fine. I even went and stuck a Ford emblem on the back with high hopes, didnt help.

Ok, start over....think, act
Step by step

Coil
Ok
I went to Dodge. I bought a Mopar coil pack, and had them meet me outside on the street because I won't even walk onto their lot.
I went home, 5 minutes I put it on. I then Googled the Drive Cycle for a 2004 Dodge Neon and spent about 1.5 hours completing it, thoroughly, twice.

I checked with Forscan, all monitors had completed.

I instructed my daughter to run the a/c full on, everywhere she went and to text me immediately when it idled rough, stalled, ect. She has a 10mm socket/ratchet in the car and knows how to reset the ECU so I wasnt worried. I forgot about it, and 3 days later I reminded her that she didnt tell me. She said she will when it runs bad.

It has been a month.

Anyway, I got way off on a tangent of passion there, but I think it was necessary.

I will turn this back over to the OP and pawpaw...

 

I changed all ignition as I've had bad ignition coils on this all the time. Nothing changed. I did check the timing and compression. Both were good. At the start of all this trouble fuel pressure was right at specs of 65psi. Now it is down to 56psi and needle radpidly fluctuates. So the shop recommended to replace the fuel pump. It's 2 years old and under warranty so I'm going to try. I'm running out of options except the entire engine. But I'm sure it's something a lot less costly. However my Dodge Dakota R/T runs 100% better than this. I just don't drive it often because it's 1 of 501 made in 1999 and it's mostly a cruising truck. Taken it a few shows too. It's a lot more fun too having 204 more ft-lbs of torque. It doesn't labor up all the hills like my Ranger. But my Ranger is my daily driver.

 

Update again. We changed out the fuel pump under warranty. It didn't help the idling problem. But I've heard a noise that concerns me under the hood. I've heard it before but it could be a different noise that sounds similar. At idle you can't hear it. If you're in Park and idling you can't hear it but if you rev it up it makes a thumping noise down around the middle of the front of the engine. Last time it made a sound like this the timing belt tensioner was bad. I replaced both maybe 30-40,000 miles ago. I don't think it's a rod knock. It sounds like something is hitting something. If it's a bad timing belt tensioner is there a way I can tell if it's bad besides taking off the whole cover? I sure hope it's not a rod knock. It still has no power.

 

Post a audio file of the sound & maybe an engine guru can identify what your hearing.