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All right, I'm gonna do it. I have been searching off and on for a while now with no success, so I am just going to ask.

I bought a 97 civic LX with a non-stock motor. The block is stamped D16Y8, but there is no vtec solenoid, so I am guessing it is still the Y7 head. OK, so basically I have an automatic D16Y7. Got it.

I have since done this maintenance on it:

- Replaced the coolant hoses with silicone hoses because I kept popping the old rotted ones
- Replaced the radiator with a bigger all aluminum unit
- Replaced the thermostat while I was at it

I then decided to replace the IM with a D16Y8 unit because I got a good deal on the Mani and the TB. I replaced the rotor off my automatic Y7 TB and reused it. I basically kept everything that was on there and replaced JUST the mani.

I replaced all the hosing and the PCV valve while I was in there, and used a new IM gasket when I bolted it back together. I went through the procedure to re-learn idle after the replacement

OK, with all that back story, here is my issue. Let me start by saying that 95% of the time the motor runs EXACTLY as it should, especially when it is cool out, but I will get to that.

Sometimes my idle surges. I think surges is the proper word. I will start the car up cold and the idle will drop just as it is supposed as it warms up. I can drive around and every stop light, stop sign, and when I reach my destination the idle is just fine.

HOWEVER, if I sit in traffic for a long period of time, lets say I'm doing the 5PM rush hour crawl for a mile or so (lets say 20 minutes) my idle will slowly creep up from 800-900 up to about 1100-1300. Once I get moving again, the next time I slow down it is back down to where it should be, around 800-900.

The other time I notice it is when it is HOT out, like 90+ degrees. If I hop in my car, start it up, go to the store, run inside, and come back out and start it again the idle will shoot up to 1500+ RPMS right from the get go. If I do this multiple times, lets say from store to store, it compounds. One time I got in after bouncing in and out of shops and started the car and the idle shot up to 3000 RPMs, like what?

Occasionally if it is really hot, it will happen right from the cold start up, but that is not very often. Just a high idle that doesn't drop down as the car warms up.

A few of my theories:

IACV? I have taken it off and cleaned it as well as I could with brake cleaner. The problem persists.

Not enough coolant? I check my fluids weekly, and when I first changed out all the coolant parts I ran the car with the front on ramps to try and get all the air out, then topped off.

Radiator fan DOES run, at first I thought maybe it wasn't running and letting things get to hot.

I have taken the TB off and checked it over multiple times, as far as I can tell it is working just as it should.

I'm out of ideas. The weather in Georgia right now is cool fall weather, and the issue only happens when I sit in traffic for a long period of time.

The car runs exactly as it should the rest of the time. No other issues at all to report other than a leaky power steering system.

Here is a picture of the bay just because threads without pictures suck.
 

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