Hello everyone.
I have a 2000 Honda Civic EX 5-speed.
Pretty much all stock other than headers \ exhaust \ CAI.

Now the issue I'm having is the old hunting \ surging idle when warmed up.
I actually found the twice removed previous owner on this forum but have been unable to reach him directly. (Old phone # \ hasn't responded to private messages)

From what I can tell he performed a Y8 intake swap from an earlier engine \ polished it \ perhaps cleaned up the runners \ capped off the air injection holes.
They also mentioned adding an Integra throttle body as well.

Well that's all fine and dandy but now that I have procured this vehicle I want the surging idle fixed because it's annoying as hell.

It will hunt up and down, and occasionally idle super low. Like 500 rpm or lower
Here's the car running -- https://photos.app.goo.gl/lFAEH2WAOjFaL8Bf2

I've replaced the IACV and unplugged the battery for a whole day.
Can someone please let me know which sensors the ECM is using to control the IACV?
If I need to replace them that's ok but I've scanned the OBD and there aren't any stored or active alerts.

Thank you! -Chris

 

I would look for leak. Especially around the throttle body, the tb cable clamshell. Mine was leaking slightly from over coiling of the coil therefore idle was crazy.
i suggest using smokes to find the leak. At night time is best. Smokes show up pretty clearly under the light, inside the garage if possible so no wind.

 

Make sure you have the proper EX manual ECU and two-wire IACV. Check that cooling system is completely full (look in the radiator with engine cold). Have someone slowly press and release the gas pedal (engine not running) while you check that the throttle plate returns to fully closed every time. Check that TPS voltage is 0.4 with throttle closed. Check ECT sensor with ohm meter. Check that rpm always drops to below normal idle with IACV unplugged.

 

Hey.

That's my old car for sure.

I PMed you.

 

Ok I'm back, sorry I had to put the repairdiag on hold for a bit. (I'm going to verify the ECU tonight)
So the TPS has good steady voltage, ECT reads steady, and the TB functions pretty well but it is older and dirty.

Being that this may or may not be an intake or TB leak I went ahead and bought an S2 Intake Manifold 66 mm S2 Alpha throttle body TPS MAP ECT.
The IACv is brand new so I'll just transfer that over. (The car has the same problem regardless of which IACv is used new or old)

I will say this happens only when the engine is at full operating temperature.

The car still has the surging idle but now what it does is after driving for 15 minutes or so and coming to a stop it will occasionally go into this fast repetitive idle loop "woop, woop, woop, woop".
If you shut off the car, it will drive for another 5 or 10 minutes and then right back to the idle loop.

If you attempt to add a small amount of throttle, the idle won't change.
Give it 1 or 1 push it will rev super fast on it's way to redline. (but I release the pedal before that happens of course) As if the TPS isn't functioning but according to the diagnostic app the TPS range is gradually climbing as it should.

I took these screenshots of when that "woop, woop, woop" idle loop is occurring.

https://i.imgur.com/hWGA3rF.png --------- https://i.imgur.com/e6cwIo2.png
https://i.imgur.com/UR0hZei.png --------- https://i.imgur.com/uQj4TDU.png

• You can see that the engine is at operating temperature.
• The gauges show that the short term fuel trim sweeps from 0 to 7.8 back and forth. (I'm going to see if I record the screen next time)
• Also noticed that the Fuel System Status swaps from Closed Loop to Open Loop back and forth.

The only check engine light is (P0505 OBD-II Trouble Code: Idle Control System Malfunction)
The beast.