schpiel

Looking for any advice that may lead me to solving this problem. 1996 Honda Civic Lx. Factory d16y7 with manual transmission. Removed motor to freshen it up with all new gaskets, seals, and put new clutch and flywheel in. Motor went back in and is running with no issues besides this roaming idle. Not one CEL is being thrown either. I start the car cold and it instantly registers at 2k rpms. The idle then drops to 1.5k and revs up and down between 1.5 and 2k. I have read all of the help threads about the IACV and have performed the clean on it and saw no results. I have also removed throttle body and gave it a good cleaning as well as installed a new gasket. Then I reset/relearned the ECU. When I cleaned the IACV, I checked to make sure that the valve spins freely and it does. I am looking for any advice! Thanks

Former User

Does the CEL work?

When the idle is misbehaving, remove the air intake system and then use your finger to cover the port/hole inside the throttle body leading to the IACV. Does the idle speed drop and settle?

schpiel

The CEL works just fine. When I cover the port on the IACV it does not affect the idle. I have read that this may mean that the valve needs to be replaced. I am just perplexed how I did not have this issue before....

Former User

You should have added this^ to your first post.

No it means there is a vacuum or intake air leak. Start by checking for a vacuum hose that may have been disconnected.

schpiel

Thank you sir. Engine has cooled off again. Time to start hunting vacuum issues! Will post results.

schpiel

Okay correction, when I cover the port in the throttle body that is on IACV it slows the idle down and stops fluctuation. So what next?

Former User

Start by trying to adjust the idle speed. See Diagram in FAQs sticky.

schpiel

I feel like the idle screw was all the way tightened in? I am going to read thread now

schpiel

Okay, so adjusting idle speed did nothing for the car. I have determined that there has to be a vacuum leak of substantial size somewhere. So far I have tested all vacuum nipples running to intake manifold, including pcv system and brake booster vacuum source. What else could it be?

Former User

What makes you jump to this^ conclusion?

This^ tells you that your conclusion is wrong.

Test the ECT sensor and TPS.

schpiel

Because with the intake tube off of the car, when I place my hand completely over the throttle body, cutting of its intake supply, the motor continues to run. It has to be pulling vacuum from another source. I am thinking the intake manifold gasket did not seat properly or that when I removed fuel rail assembly from intake, one of the sealing o-rings cracked, and is allowing air into the intake. Gonna hit it with the ether after work, around those areas.

Former User

These^ two different test results tell you there must be two separate problems - (1) too much IACV bypass and (2) an intake air/vacuum leak.

schpiel

So a quick spray test around intake manifold showed that the vacuum leak was coming from it. Checked the bolts, they were barely tight. Must have forgotten to torque em all the way down when replacing gasket. Will tighten down the bolts all the way tonight. Feel stupid for this being the reason for the issue. Haha. Guess I overlooked the common sense stuff. Thanks for your help man!

Jimster480

its often the most common of stuff that causes the problems. I had a similar problem (and you might want to check this too) on my injector seals, one of them was leaking on the underside of the injector where I couldnt see it, and it was driving me nuts for like a week before I found it.

schpiel

You're exactly right man! Just got out of work and ready to tighten down this manifold. But when I was talking to the old school drag racer at work, he was like "I'll tell ya another place to check for them leaks is on those fuel injector o-ring seats into the manifold!" Haha. Dude has a wealth of knowledge!

schpiel

Update...snugged down intake manifold and replaced injector o rings. And still idle issue.

Jimster480

hmm, spray soap water over everything and see if there are any other leaks. TB or IACV gasket maybe?