lilbeast

I know there are numerous other threads about this but I am making this one because I've simply tried just about everything I've read in those threads and just about everything I can think of.
I recently found a y8 AUTO manifold from a junkyard with NO COLD START ASSIST, cleaned it up, and swapped it on my 98 Civic LX 5 speed with the y7 manifold. The car now idles at about 1200 at the lowest, and when I give it ANY throttle whatsoever, it likes to rev up high and just sit there for a few seconds, then it will go down. A lot of times when it goes down, it's like the car will almost die, then it comes back into it. It will idle normally (just high) if you don't touch the throttle at all.

I've done many things to try to solve this issue so let me just list them off:
Checked vacuum leaks, none. (car will also die if I cover up the TB with my hand)
Replaced PCV valve
Replaced IACV
Reseated fuel injectors and o-rings
Bled coolant, numerous times.
The cruise control nipple is capped off.
All electrical connectors are hooked up to the correct spot (even double checked the wire colors with the honda manual)
All coolant lines and vacuum hoses are going to the correct spot.
Reset ECU (unplugged FI E/M fuse for about 15 seconds and put back in. Also tried to reset ECU by unplugging battery after idle problem persisted)

I could be forgetting something up there, I've spent so much time trying to figure this out


ALSO: the car will act perfectly fine if I cover up the IACV port inside the throttle body.

Anyone know anything else I should try or have any advice to offer? I'm really at a loss here

mk378

If blocking the IACV air hole makes it slow down, the problem is there. I thought that the 3 wire ones on the manual EX were compatible with 3 wire from a DX, but maybe not. The idle speed depends on correct readings from the ECT. If the ECU thinks the engine is cold it will open up the IACV to make it idle fast. You can check this with a scanner that reports live data from the sensors.

Any time you cut the battery power to an OBDII ECU, it has to recalibrate itself over several minutes of running. During that time the idling will be inconsistent.

civic402lx

What year was the y8 manifold came from?
did you swap over everything from y7 onto y8 manifold?
what throttle body?
did you do the throttle body snail conversion?
are you using stock y7 tb cable?

tony_2018

Make sure you have every harness connected.

lilbeast

I actually found out what the problem was. The throttle rotor I swapped over from the y8 tb was actually broken and I hadn't realized it. The rotor "hat" on the backside had broken off of the plate itself. It seems like this is common to happen since when I went to the junkyard I pulled off another that broke. It must've been getting in a bind causing the throttle plate to stay open or slam close intermittently. But all in all, the problem is fixed, I appreciate the replies I got and thank you for your help