Last year I installed a DP nitrous kit on my girlfriend's '00 Integra. Due to time constraints (right before the NOPI Nationals), I had to do a core swap for the intake manifold with a local shop. Basically, they tapped a manifold they had in stock, and I installed that one. Had some vacuum leaks around the gasket, replaced that and car ran fine. This past April, we did a turbo setup on the car and the problem came back.

Here are the symptoms, sometimes at idle, the car will surge like crazy. I mean it acts like the car is hitting fuel cut at 1500 rpm. On the AFC, it's showing a surging between 1450-1520 rpm and it's doing it really, really fast. It's almost like bouncing the tach. The tach doesn't move hardly, but we can see it vibrate a little. It doesn't do this all the time, it gets worse when the weather gets colder. I once again replaced the IM gasket and this time I also pulled the IAC valve to check it (there was a ton of carbon buildup in there) since the car was throwing CEL 14 which is the IAC valve. I unhooked the IACV and the car idled smoothly at about 500rpm. I was told this means that the IACV is working. The problem went away for about a week, perfect idle. But the past few days, the temps dropped and the problem came back even worse.

I can't seem to locate any more vacuum leaks, it reads 20 hg at idle, which is what I've seen other Integras/Civics read. What other things should I check for? The car is a daily driver and it is driving us crazy. When driving, it's fine but when coasting to a stop, it will surge also. Pretty much anytime the car throttle body is closed. Is the IACV bad? The car only has 38K on it. And currently, the coolant lines to the throttle body and IACV are bypassed to run coolant to the turbo. The car was doing this before the turbo install, so I'm thinking it's not that. But I'm all out of ideas.

Sorry for the long post, thanks for any insight into this problem.

 

Sounds like the IACV to me. It's use for cold starts by checking water temp as the temp rises the IACV drops the throttle. I suggest replacing it first, if you all ready tried cleaning it with carb cleaner. It will only do it again. An easy way to check for vacum leaks is to spray carb cleaner on vac hoses and connections. You car will idle high for a moment then settle back down.

 

I guess it's time for a new IACV then. I've already done the carb cleaner test, and it's not finding a leak anywhere. Thanks.