So to catch you all up with everything I've done so far:
Bought this 98 4 door lx... non-vtec so y7 code
RACV circuit code up.
Cleaned the IAC valve and noticed the wrong gasket on the throttle body letting a major amount of air into the intake.
Also noticed someone had tweaked with the TPS and cranked it up to about a 45% reading at an idle.
Fixed both issues and still a RACV malfunction.
Tried a few IAC valves, no difference. Tried a friend's computer, still pops up.

Then decided it must be in the wiring. I had a 98 EX y8 taking up space with a fresh head on it so i said what the hell might as well. Swapped the head, engine wiring harness, computer and exhaust system. Keep in mind this EX did NOT have the code up for the RACV circuit malfunction. I haven't yet wired in the 2nd O2 sensor but it's in the works.

Fired up fine today but got the dreaded RACV circuit code!

It seems like the idle is running a little high... haven't warmed it up all the way yet but wanted to check the code and it's still up even after putting a known good head, harness and computer into the car!!!!!! WTF!

Just wondering if anyone on here has run into a ghost problem like this, or if there's a possibility that there's a gremlin in the body wiring somewhere?? I'm almost at my witts end here, any input would be great! Also noteworthy I tried erasing the code with my bosch scanner and it won't go away at all before and after the conversion.

 

So... I figured out one problem. Turns out I had a slight dumbass attack and put in the lx ecm instead of the ex ecm. However radiator fan still isn't working and now its surging instead of kicking down the isle so its still having a bit of a problem. Going to swap out the temp sensor for the fan tomorrow and go from there

 

Hunting idle can be caused by low or improperly bled coolant. Unfortunately, because your radiator fan isn't working, it's not possible for you to properly bleed your coolant in the first place. Before you start randomly replacing parts, test them. Do you have a voltmeter, and are you capable of boiling a pot of water?

 

Yes and yes. I also have a complete parts car that exploded the bottom end but everything else works.

 

Well in that case, swap the thermostat and fan switch over from the parts car, bleed your coolant with the below procedure, and see if that helps. Keep an eye on your temperature gauge while you're doing this so you don't overheat.

Secure the front of the car on jack stands, or park it facing uphill. Remove the radiator cap. Start the car, and let the engine idle for two radiator fan on/off cycles. It should take ~15-20 minutes, but might take longer in colder weather.

If that doesn't help, I'll post some FSM pages and give you some things to test.

 

That was the plan. Temp gauge on the new si gauge cluster never read over half but my code scanner was reading the temp at 230ish hoping the new switch runs the temp gauge on the dash

 

Those are completely different sensors. There are three sensors that look at coolant temperature. The first is in the coolant neck where the thermostat is, and that one is the fan switch. The second and third are both in the head under the distributor. One is a single wire sensor that controls the cluster. The other is the actual coolant temp sensor, which feeds data to the ECU. IIRC, the thermostat should open at ~170F, and the radiator fan should turn on at ~190F. "Not quite halfway" is normal operating temperature for 96-00 Civics, but the cluster gauge is also horribly inaccurate.

 

So finally got another day off and here's an update.
Swapped out the switch with a known good one. It's a no go.
Jumpered the wires in the connector with the key on and no fan.
Jumpered the relay, fan works, no 12v on the control side of the relay though...
Working on checking the wiring under the dash...
Another issue I noticed today is i'm not getting power to the climate control interface, and I'm starting to think the two issues are related. Will post back when I know more.

 

So... finally got THAT figured out, in a way. Ended up pulling out ALL the fuses under the dash and put them all back from the diagram on the cover. My guess = bad connection on one.

Now I have a fluctuating idle/fast idle. Going to clean IAC valve again... My TPS reading seems a little high too. It's at 11 (live data from code scanner). I checked this against my other civic, it's reading 9. Either way the idle doesn't seem to be dropping where it needs to be at full operating temp. It drops from ~2000 when I first fire it up to ~1300, sits there for about 30 seconds then fluctuates from ~1700 to ~800 rpm. I don't think the car this head and wiring came out of had this issue at all, but I'm not really sure what my brother did to it before he blew a piston out of it.

Code up is P0505 (idle air control)

 

Do this and report back.

FYI - P0505 may be a mechanical problem with the IACV but not an electrical problem in the IACV circuit. Other causes are also possible, such as vacuum or intake air leaks, improper idle speed adjustment, or ECT or TPS circuit problems.

 

Turns out I missed a vacuum line that runs the cruise control. Hooked it back up and now she's purring nicely at ~850 RPM. Sounds like she has a really random miss though... could it be the distributor? I think this one has about 200K on it. Tried running the original distributor but the bolts snapped off in the aluminum housing holding the cap on. I could get them out but found a distributor for about $190 and would rather go that route to know I have a good one. The warmer the car gets the more frequent the miss is. I have new plugs/wires/cap and rotor and the coil has been replaced recently. No codes have popped up yet. Will update if I get any.

 

Compression test the cylinders.

 

Also is the heat shield really necessary on the exhaust manifold? The one I have on this car can only be held on by one bolt so it rattles like crazy. I'd like to just leave it off if it won't hurt anything.

 

I don't have the best compression tester in the world but here's my findings:

#1 191 PSI
#2 189 PSI
#3 190 PSI
#4 194 PSI

 

Turns out the new plug wires were bad?!?! Put the old ones back on the misfire went away but now I'm getting a code for the knock sensor wtf? Other than that car is running great thinking about getting the smog test done next week to see where I stand.

 

They probably weren't seated in all the way.

 

Reset ECU to see if KS code returns.