90si-rex

Got an idle issue in my 2000 civic ex, d16y8, no mods. I just rebuilt the motor and it starts and runs but the idle is terrible. Basically what happens is I'll start the car and it idles fine for a few minutes, then the idle will drop almost to the point of stalling. It'll run like that for 30 seconds to a minute, and then the ecu catches it and raises the idle back to about 750 or sometimes a bit higher, and then the idle drops out again. It has a brand new iacv, fuel filter, fuel pressure regulator, plugs, wires, distributor cap and rotor, and air filter. I haven't been able to find any vacuum leaks either. I really need to get this solved today because I can't afford to keep using uber to get back and forth. Any help is appreciated.

civic402lx

Try smoke test to find leak. Check tb gasket.

90si-rex

Not sure what you mean by smoke test. Also probably should have mentioned that the tb gasket as well as the IM gasket are both new as well.

09chaplak

Idle adjustment screw? Does it smell like gas really bad? Make sure you didn't switch the TPS with the MAP sensor.

civic402lx

Search YouTube for the using smoke to find leak video. You will see what I mean. Last time I had an air leak it was so small there was no way to see it. Once smoke was introduce, it was clear as day.. Fix the leak, idle back to normal.

You should not play with the idle screw until you can confirm there are no air leak..

09chaplak

Did you check the cruise control little plug in the back of the manifold?

mk378

Have you driven the car or let it run for a long enough time (about 20 minutes IIRC) for the ECU to recalibrate?

Also if your backup fuse is blown the ECU will lose calibration every time you turn the key off, causing it to idle poorly on every start.

HoangR

I agree with 09chaplak question. There is a small black vacuum hose that can commonly comes unplug, check to see if your cruise is working. If not, that might be your problem/solution.

90si-rex

I've double checked all plugs. Everything is plugged in where it should be. I did drive the car for about 20-30 minutes and it seemed ok after that. Went back out about an hour later and did a relatively short trip up to the store, and it was bogging down again. Tonight I drove it for about 20 minutes and it was bogging down, but then after that it seemed to run pretty well with minimal bogging down. It seems like if I let it warm up for a while (20-30 minutes or so) and then drive ti there's less of an issue.

I'll try the smoke test as soon as I can because it sounds like that has the most potential to point me toward any leaks.

I also have a CEL for the primary O2 sensor. Any chance that could be at least a partial cause for my issue?

civic402lx

I would replace the o2 sensor anyway if its bad. It will effect your fuel mixture and economy.

As for the smoke test. The cheapest route is have a friend that smoke help.
Unplug the brake booster vac hose at the manifold. Get some tubing that fit over the port where the brake booster hose was. Take the air tube/intake off. Cover the throttle body oening with some latex glove and clamp the clove down. You want the glove to expand so you can see its getting air.

have your friend puff some CIG smoke and blow into the tubing that hooked up to the manifold. Keep doing it til the glove expand. Best to do it inside the garage with no wind. Use your spot light and keep an eye out for any smoke coming up and out around the throttle body gasket. Intake manifold gasket. Any where vac tube are present. Make sure your friend stand away from the engine bay while blowing smoke into the tubing. If he is not bowing smoke through the tubing, he need to use his thumb and plug up the tube. That way it will keep the smoke inside the tube and manifold.

I had to do that all by myself and I don't smoke. Found the leak though.
Look very closely. Some leak can be very tiny, hard to spot unless u look directly over it. Go slow and work from the throttle body over to the driver side.
But if u have a smoke machine then it would be so much less work. More smoke, easier to see leak.

90si-rex

Thanks. I went ahead and ordered the o2 sensor so I'll replace that this weekend. I'll give the smoke test a try and report back.

CX-Adam

I'm going to try this tonight on my car. I don't have anyone to help, though. If I can't get the cigar/cigarette method to work, I've got some old paint cans, bike tire tubes, mineral oil, and hose barbs lying around. I might try and rig up a DIY smoke machine.

mk378

Did you read the second sentence of my post?

Also you have to fix the O2 sensor, the calibration process is based on readings from the primary O2 sensor so it needs to be good. Don't expect any car to run properly with the CEL on.

civic402lx

Give it ago. The leak on mine were the throttle body clam shell spring/coil. Directly behind the coil. Apparently I had over coil the spring just enough to cause a leak. Did this when I swapped y7 to y8 manifold, had to use the clam shell from y8 so the tb cable would position normally. That is what caused my idle to go crazy. I even spray it with carb cleaner, on cold start only, and didn't see any change. Once I did the smoke test, i can see the smoke slowly leak out behind the coil. Loosen up the coil one turn and it seal perfect. Idle perfect ever since.

Good luck with your smoke test, hope u find the leak.

90si-rex

I did read the second sentence of your post, just forgot to address it when I replied. The back up fuse is good so I don't think that's contributing to my issue. I have a new o2 sensor coming. Should be delivered tomorrow.

Jimi Hondrix

Did you burp coolant properly?
Compression good?
Can pull fuel rail and spray injectors into a bucket to watch for pulse and spray pattern

90si-rex

Coolant was burped properly and compression is decent across all cylinders. I could pull the fuel rail and spray into a bucket but I'd rather not unless I absolutely have to. I did go ahead and replace the backup fuse tonight just for ***** and giggles since it's cheap to do it and that didn't seem to make any difference. Next up will be the o2 sensor and smoke test since those are easy.

Jimi Hondrix

Maybe fuel pump isn't woorking properly/ incorrect fuel pressure or intermittent.

CX-Adam

So, it only idles rough after it's come up to temperature? If yes, how low is the idle? 550 rpm or less?

With the engine running, try disconnecting the IACV 2P connector. Does the RPM drop or does the engine stall out? If yes, adjust the idle speed. If no, replace the IACV (try cleaning it and making sure you've a good seal first).

The IACV only controls RPM at idle (throttle plate closed) which might explain why it's OK when driving.

I'm currently diagnosing a similar issue and I just found a HUGE vacuum leak which should be the cause of most of my problem(s). But, I've gone through all the other idle control procedures.

90si-rex

Yeah, pretty sure I have a leak somewhere. So initially, it would idle high when I first started it, and then after a few minutes the idle would drop to about 500, maybe less before the ecu would catch it. After it got warmed up it would hesitate a bit but after being driven 10-15 minutes it ran relatively normal with just the occasional stumble. The last couple of times I've driven it it's never gotten to the point where it's close to normal. The idle keeps dropping to about 500 or less, the ecu will catch it and raise the idle to somewhere around 750-1000 and then that cycle just keeps repeating. I have to constantly stay on the gas to keep it from bogging down. This means stopping as little as possible (nearly impossible in city traffic) and pulling the parking brake and blipping the throttle to keep the rpm's up when I do have to stop. Super annoying.

Today I decided to pull the codes for the hell of it and in addition to the code for the o2 sensor that's being replaced this weekend, I now have a p1399 as well. Everything I've read for that one says to do a valve adjustment and the problem should resolve itself. I also plan on doing a smoke test this weekend to check for any leaks.

It has brand new plugs, wires, cap, rotor, air filter, fuel filter, and iacv and probably a couple of other things that I'm forgetting.