95 hatch, manual d15b7. Surging idle between 900~1000-1400. Unplugged the iacv and it throws CEL like it should, and the surging stops but then idles at 1500. The high idle indicates a vacuum leak, right?
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Yes. When you unplug the IACV, it should spring shut which causes the idle to slow way down. (A code 14 is thrown immediately whenever the electrical circuit is opened.)

Make sure the throttle plate fully closes when no one is pressing the gas. The throttle cable should be slack. The screw stop on the throttle body is factory set for the plate to close fully and must not be tampered with. That screw is NOT used to adjust the idle speed.

The next thing to check is to pull off the big hose from the air cleaner at the throttle body. Note there are three holes in the side of the throttle body before the throttle plate. With the engine warmed up and idling, hold your finger over each one to see if air is being pulled in.
Bottom hole -- FITV, should be closed because engine is warmed up.
Middle hole -- IACV, should be closed because unplugged.
Top hole -- Air bypass screw valve -- this should be the only one pulling air, and if you block it the engine should stall out.

 

I only have two holes in my TB. With IACV Unplugged car idles at about 950-1050, no noticeable surging. With the top hole plugged the car idles at about 850-900. With the car warmed up, so the fans come on, there is no vacuum in the bottom hole as expected. What does this indicate?

 

I may be mistaken but sounds like your IACV.. If it is out of the equation and car runs as it should, I'd think that's a problem. **shrug**

 

When I plug both holes and have the IACV unplugged though the car is supposed to die but I checked again today and it only drops down to about 500 RPM so I'm not sure if this indicates a vacuum leak or not. With the top hole plugged though and the IACV, plugged in, the car idles right around 600, so based on this alone it seems like IACV but the idle fluctuates almost all the time even when the car has just been started in the morning.

 

It stops surging when the A/C is on or when I push in the brake. Would this still indicate an issue with IACV?

 

You need to get it so it idles considerably slower than normal (450 rpm) with the IACV unplugged and A/C etc turned OFF. Find out where the air is getting in. The connection to the brakes means the brake booster could be faulty, disconnect the hose and plug the opening in the manifold. It could also be just the additional load of the brake lights.

 

I tested the brake booster according to the factory service manual, and it seems to be ok. I sprayed carb cleaner everywhere, but I'm having trouble locating a vacuum leak.

 

Get a smoke machine. Tne leak, if any, will be visible clearly.

 

I know getting a smoke machine would be ideal, but its not feasible for me, as I don't know where I could rent one, and don't have a garage. Based on my symptoms though, does it seem like it's more likely to be a vacuum leak or a bad IACV?

 

A bad IACV is a vacuum leak. Anything letting too much air into the intake will cause idle speed to be above normal.

 

buy a heap cigar. Have your friend huff and blow smoke into the intake manifold with a couple foot of air tube hooked up to the manifold. Block the throttle body with rag or glove.
its on youtube, scott kilmer have a vid on it. Look it up.

 

Thanks. I should've been more clear, a vacuum leak from somewhere else besides the IACV, since it happens even when the car is cold. For some reason if it's not happening, I can make it happen by revving the engine to 3k or so and it starts. I'll try pulling it off and cleaning it today

 

Sounds like a bad iacv.