1sthonda

I don't have any CEL

Problem 1:
When I show down and put the car into neutral or down shift the RPMs go to 500 and then quickly back up to 1000. I notice this mostly when I'm in the higher gears. I thought it was the TPS, so I replaced it with a used one. Ohms tested out okay. 0.5 ohms at closed and 4.5 ohms at WOT. However the problem still occurs.

Problem 2: The RPMs will jump as bad as 900-1400 but usually closer to 1000-1300. This happens on a few different occasions. Mostly when rolling in neutral. It's not regular. If i brake hard to almost a full stop it can set off the rolling RPMs. I feel like the lights are somehow tied into this because I notice it mostly when I have the lights are on. Also, the car will idle at about 1100rpms with the lights on. When I come to a complete stop and turn them off they will go to about 650RPMs. Then if I turn them back on the RPMs will go to 800ish. Once driving again for a little while the RPMs will be back at 1100 when in neutral or at a stop sign/light

There has to be a vacuum leak somewhere right? I can't locate it. I've pulled off the intake and put my thumb on the IACV port and the engine turns off. I also ran an unlit torch (propane) around the vacuum lines but there was no change in engine noise.

Problem 3: The car also seems to take a long time to warm up. 1500 RPMs when first turned on, and it will stay there until about 10 minutes of driving. Its fine if I'm in gear, but when I'm stopped at a light the RPMS are just at a steady 1500. Thought it was a temp sensor, or thermostat but the heat blows hot enough, and the temp sensor reads in at about 8:00 or 8:30. How long is it supposed to take for a car to warm up? RPMs at 1500 for 30 - 90 seconds is fine, but 10 minutes is a little much.

Vindicator9000

It doesn't necessarily have a vacuum leak.

There are 3 things that control the idle on Civics, and 2 are interrelated: Vacuum, coolant, and IACV.

Generally (but not always), if you have a vacuum leak idle problem, you'll get a regular up/down/up/down idle. I mean, it moves up and down at a more or less regular pace.

It sounds more like a hunting idle problem. Since your car seems to have problems coming out of fast idle, I'm thinking there's a coolant problem.

The IACV is controlled by coolant temp. When the coolant is cold, it opens further to raise the idle. When it's warm, it closes to lower the idle. If there are air pockets in the coolant lines, then it will behave unpredictably.

So, the first thing I always tell people to chase down idle problems in Civics is to look at the coolant for signs of oil, and oil for signs of coolant. Headgasket failures often first manifest themselves as idle problems before anything else. It's probably not a headgasket problem, but that's usually easy to check.

Next, I'd advise bleeding the coolant to make sure there is no air trapped in the lines. With the engine cold, remove the radiator cap. Turn the heater up full blast and start the car. Let it run for 30 minutes, or 2 full on/off cycles of the cooling fan.

If that doesn't fix it, it could still be a headgasket problem, or maybe an IACV problem.

1sthonda

The head gasket had crossed my mind because when I first got the car there was a small coolant leak. There was very little coolant in the reservoir, however the radiator was plenty full. I fixed the leak, filled the system, and then bled the coolant of air. A few days later I saw that the coolant reservoir had lost about half of the coolant that was in it. I didn't know where it went. The oil doesn't have coolant in it and vise-verse. Could I have a leak thats going into the exhaust? No white smoke yet.

Also, the problem didn't start until after I cleaned the IACV for the first time. First problem was high RPMs at 1500 until warm. I took it off 3 times to clean if and each time I probably got air into the system because I started to get hunting idle.
-So is there a temp sensor in the IACV that I could have broken? 320k miles on my IACV, but I replaced it with one that had 130k miles on it. Still have the same problems, plus the added hunting idle. The OHMS tested 11 on the "new" one, and "10" on the old one.

EJeff8

1. A/C, brakes and headlights put strain on the engine, so that's why your idle drops on those, but the engine should always compensate.
2. Are you sure the coolant lines running from the IAVC to the IM are on snug, look good and are not leaking?

Former User

Does the CEL work?

-Clean and adjust the FITV
-Clean the IACV
-Bleed the cooling system
-Measure the resistance of the 2-wire ECT sensor under the distributor

Then go from there.

1sthonda

Sounds stright forward, but do you have a diagram on how to do this? What values am I shooting for? OHMs volts etc.

Former User

Does the CEL work?

Run the engine until it is fully warmed up, and turn off the engine and unplug the ECT sensor. Then measure resistance across the two terminals of the sensor. It should read 200-400 Ohms.

CivicSi95

can a bad ect sensor cause fluctuating idle?

Former User

Absolutely

1sthonda

Okay I checked Ohms and it moves inbetween 209.5 - 214.3 when fully warmed up. Is there a cold Ohm reading I should take into account as well?

I think I might have air getting into the system somehow because a little still comes out of the bleeder vavle. I check it just about everytime I park my car. I don't see any leaks. Is it possible for air to come in from the radiator cap? I read that they can be faulty sometimes.

1sthonda

Okay it might not matter, but then again I'm having the problem when the engine is cold. So with it being 55 degrees F outside I got a reading of 3.41 K-Ohms.

Gregg Faulmann

Hi, I am having a similar problem, I am a new first time honda owner of a 97' Civic Vtec. When I am driving like a normal driver (+/- 80km/hr) not going into Vtec at all the car drives fine, however, as soon as I go into Vtec and slow down to turn around, the cars revs just die under my foot, if I try to pull off slowly, the car will go, then the revs will die again, take, and die again of which this is ongoing. I then have to pump the acceleration all the time to drive so that the revs dont die. The revs die up to 1000RPM and stays there, so the car does not switch off but the revs die. any advice?

fv8s

i do not think the OP will appreciate you posting like that on his thread. try creating your own... https://honda-tech.com/newthread.php?do=newthread&f=1

D114

have you pressure tested the cooling system?

93del

i have the same problem with the idle

1sthonda

No, I haven't. Once the car run for a little while the hoses are rock hard.

However when I was bleeding the system a little while ago I noticed that the hoses could almost be pinched closed. I also noticed that every once in a while the coolant would stop coming out of the bleeder hole, and instead suck in air. What's up with that?

Former User

You may have a blown head gasket.

1sthonda

Crossed my mind. What's the best way to test for that?