1999 2.3L 5-speed sedan, custom blue pearl
1999 2.3L 5-speed sedan, purple raisin (parts car)
2000 2.3L Auto, sedan, black (borrowed from friend until i sort this out)

One day I was on the highway in 5th gear, when I pushed the accelerator to the floor there was nothing but hesitation and stumble. I was only able to maintain speed or accelerate by feathering on the gas pedal. I barely got the car home and it sat for 30 minutes before I tried to move it again. At this time there was no issue and I was able to rev it smoothly all the way up. Ordinarily, I would wait for an intermittent issue to repeat itself before jumping in to it, but it was the Friday before the Eclipse and I was supposed to be driving 9 hours to Kentucky. I knew from this point that there was nothing I could scientifically do to prove that I had fixed the car to take it on a road trip. But, I figured I could do some maintenance. I saw that the EGR passage could be a problem, so I removed the intake plenum. The passageway was completely plugged which led me to believe that it didn’t happen the day before, but has been a problem for a while. No code has shown up for the EGR. I separated the throttle body from the intake and cleaned them. I also removed the IAC from the throttle body and cleaned it. I installed everything with new gaskets.

Since I got it put back together it has been running poorly in a different way and this is what I am hoping you can help me with:
When I start it, it revs high. Around 2000 rpm. If left to its own devices, it will gain to about 2200 rpm after about a minute and then step up again to 2500. If you touch the gas, it immediately drops and starts fluctuating between 1500 and 2000 but it will start on ts own after about 3 mins No codes are thrown.

I have tried disconnecting the IAC and pulling the #13 fuse on the right side dash panel to reset the ECU in hopes of lowering the idle.

I have been going through the Eric The Car Guy "speech" on hunting idle issues: I have bled the cooling system, and used propane to check for vacuum leaks - this was inconclusive but it was very hard to tell if the propane was affecting it with the idle raising itself and then starting to fluctuate. I cannot rule this out so I will try again today and update.

Other information about the car that could be pertinent:
My catalytic converter was broken internally from an accident last fall and has been displaying code P0420 since then, but always running smoothly. i replaced it a few days ago and there is no change in the condition described above. code P0420 was succesfully erased and has not reappeared.
I have also replaced spark plugs to eliminate them from fault, and the air filter because it was nasty.

any thoughts or suggestions would be appreciated.I don't think I'm even back to where i was before i took the intake apart and I really need to give my friend's car back. I'm running low on ideas. Thanks in advance.

 

Ok maybe the fix by Eric the Car Guy may help. It fixed my eng replacement in my 91 accord... really simple and works https://www.ericthecarguy.com/honda-...s-hunting-idle

 

Most likely you messed up the IACV. If you cleaned it by heavily soaking it in carb cleaner or fuel injection cleaner, then the possibility you messed up the sensitive parts of it is even greater. It is a pretty robust part, when left alone, but very sensitive when it gets more than that coolant flow and air passing through it. Carb cleaner up inside of it where the plenum thing and motor is can cause it to do what yours appear to be doing.

Really, those things don't need much cleaning beyond cleaning the little screen on them and removing and cleaning or replacing the little rubber gasket. The smooth surface where it meets the intake and where the gasket goes can be wiped of gunk. If you go up into it, just use something to wipe inside of it and little bit. No spraying, if you can help it.

There is a process you can do using your micrometer to check the resistance on the IACV to determine if it's out of spec. When mine died from old age some years ago, I used that process out of an old Haynes manual to confirm it was bad. There may be some other tests you can try involving pulling the plug on it and starting the car and seeing how it idles versus when it is plugged in. You can at least confirm it is working using that method.

Codes? Hit or miss on my old 93 Accord. Your OBD2 system should be better though. But still, all of those systems are great on parts inside the distributor, but when it comes to emissions parts, O2 sensor, and the like, they sometimes won't show as long as the part is still there, malfunctioning or not.