Rep Power: 0

Just bought a 97 Civic LX Sedan for $300. Car has 223k miles on the clock and had an engine put in it about 20k ago. Previous owner did not want to put a single cent more into the car and it had sat in his driveway since October 2019 when he listed it for $500. No takers. He got sick of almost hitting it every day on his way to work and offered it to me for $300.

Car runs and drives surprisingly well, and I'm sure the new engine helps with that a lot. The exterior is... Rough. Mold and moss everywhere and one of the windows is stuck down. Gotta work on that. At least he threw in the tarp for free. The interior is equally rough with almost all of the fabric worn or stained and many dash pieces cracked or missing and the steering wheel is pretty chewed up.
When I got the car it was right at the bottom of the fuel level and I put a few cans of Sea Foam through it and a tank of fresh gas already. CEL isn't even on anymore, it only had a code for an O2 sensor which I replaced for $48 same day. AC works too, after wiring in the blower motor. The power to it had never been hooked up after they replaced it.

That's neither here nor there, however. Here is the short list of mechanical problems I am dealing with:
-Exhaust manifold is cracked in the center and needs to be replaced. What is a good, cheap option which includes a spot for an O2 sensor? I can't find any at a glance on eBay or Amazon. Doesn't need to be fancy or performance, just needs to bolt on and work.
-Gasket between air filter box and throttle body is gone. Where can I get one of these?
-Transmission shifts fine P-R-N-1-2 but the shift from 2-3 and 3-3 are HARD and the TCC lockup is equally jarring. Is the TCC normal operation? Any suggestions on elongating the life of the transmission or just leave it be?
-Passenger side kick panel covering the ECU is missing. Anywhere I could get one of these?
-Has the usual Honda idle.

D16Y6 or D16Y7 I believe, and it's NOT the CVT transmission. No ABS, has cruise.

I am most concerned about the idle issue, it's very annoying and it needs to be fixed before I can fix any of the other major problems. I don't want to put a transmission in if it will rev itself and strain the new gearbox and reduce it's life, and I don't want to put front brakes on (which it seems to need) if it's just going to keep trying to pull itself so hard at idle. The car has 3 states: Hunting idle (1000 to 2500 and back down), 2000RPM, and 3000RPM. It chooses this seemingly at random, it will do any in Park or Neutral, hot, warm or cold.

tl;dr I have the Honda idle surge on a D16Y6/Y7. What should I check first?

 
Rep Power: 366

car-part.com

 
Rep Power: 125

D16Y7. Like daidoji said, I'd get the parts you're looking for from a junkyard. That site works well.

Also, that O2 sensor won't help in all likelihood. Sounds to me like you got a cheap aftermarket sensor. Needs to be OEM or direct from Denso. I suspect the one you have in it isn't actually working which is causing the idle issue.

 
Rep Power: 0

The O2 sensor I bought was a Bosch direct fit from O'Reilly's. Part number 13007. Bosch was heavily involved with the invention of the Lambda system, I wouldn't figure their sensors would be bad.

The idle issue was the reason the car sat up - It was an issue before the CEL was on, before I bought the car, how the car was so cheap, and persisted after I replaced the sensor.
The CEL was on for bank 1 sensor 1 open heater, which always comes down to replacement.

 
Rep Power: 221

Can't use Bosch on Honda's, needs to be Denso.
hit up a junkyard, clean the TB, and do 3 drain and fills on the trans, you'll need about 3 quarts each time.
Can also weld the crack, I did that on one of my 05s

 
Rep Power: 0

Ah, well the sensor is reading perfectly fine with both a multimeter and in OBDII data stream. I'll leave it as is, I'm not interested in spending 1/3rd the value of the car on an oxygen sensor.

The manifold is already welded, the weld broke in the center. I'd rather just replace it than buy / rent a welder just to temporarily fix it.

Cleaned the throttle body earlier today and no change, when I was driving home from work a minute ago the CEL came on at a red light the surging problem got faster.
Right now it revs between 1500 and 2000 and the CEL has code P0505 "Idle air control circuit."

 
Rep Power: 221

That's on the throttle body, take it apart and clean