r berq

98 Civic EX 4-door, 256K miles.
After warmup the engine often idles too fast, about 1400 RPM. The shop cleaned the IACV, but I know they did not remove it from the car, just opened the throttle plate and sprayed a lot of carb cleaner in. Idle is a little better now -- sometimes it drops to about 700 RPM when it should, other times it does not.

My question: Was the cleaning method adequate? Seems like it just sort of half worked. The IACV sits below the throttle body on this car, and I think he more or less squirted in enough cleaner to fill the passages, then let it evaporate. Should this have done the trick, or would it benefit from more cleaning? Can the IACV be cleaned successfully without removing it from the car?

Former User

Remove the IACV and clean it properly.

mikekh10a

iTrader: (2)

The best way is to remove the IACV and spray into the holes and let the fluid soak in there.
I had much success when I used Simple Green to clean it, I've heard of people using Carb cleaner too.

r berq

Do you fill the holes right to the top, like filling a cup to the rim? And why not leave the IACV right in place installed in the car, when doing that? The way it is positioned, it looks like the cleaning fluid would not go anywhere....

mikekh10a

iTrader: (2)

yeah to the very tip top. and i would rather let it soak in, rinse it out, and wash again with water just so none of it stays in when i turn on my car.

r berq

OK, that seems to have worked. I pulled the air intake hose, squirted lots of carb cleaner in the IACV ports, and while it was soaking I turned the ignition key on and off a few dozen times on the theory that would work the solenoid valve back and forth and help free it up. No water rinse, though, since I was doing this with everything still on the car!

Idles correctly now, where before it was sticking at either too high or too low RPM. I won't declare victory yet, until it works right for a few days straight with no bad episodes.

Thanks for the advice offered, folks.

mikekh10a

iTrader: (2)

as long as you attempt to search first, use good punctuation and are descriptive about your car problem, people on honda-tech love to help

tsylican

iTrader: (1)

r berq

Well, bummer! It's back to abnormal this morning, staying a about 1400 RPM idle. I'm beginning to wonder now about sensors. I have already checked the coolant temp sensor just below the thermostat, and that shows the proper low resistance at operating temperature. Also checked actual coolant temp with a thermometer in the radiator, and it stays between 195 and 210 at idle as the fan cycles on and off. What other sensors might be involved in controlling idle speed?

axis11

The best way to clean the IACV is to remove it, rip it apart and clean those tight spaces in there. Spraying carb cleaner would not clean it well enough and might just dislodge the dirt and cause the problems to return. As for your question, the MAP and TPS sensor plays a major role in fuel delivery. Vacuum leak would cause a different reading on the MAP sensor and cause rpm to increase.
I would suggest fixing first the IACV problem before searching for more problems.

Mitchness

Yeah, just remove the IACV. It's only a couple bolts and isn't that hard to get to. You'll never be able to reach all the nooks and crannies that you need to with it still on the TB. If it still won't work, try finding an IACV at a yard and see if that changes anything.

redm3turbo

^ pretty sure the advice was to REMOVE it and clean it

You'll have to redo this job at some point as you only effectively put a bigger hole in your gunky buildup. Next time...just remove it

r berq

OK, lesson learned. It's going back to the shop to be removed and cleaned, since I don't have the patience or the manual dexterity. Talked to my mechanic today, and he said cleaning it in place sometimes works, so it was worth a try -- 5 minutes labor as opposed to an hour or so. Of course then there was my 10 minutes labor on top of his 5, since I figured maybe I could do it when he couldn't, after all he's only been doing this for 40 years.

r berq

Update: IACV was thoroughly cleaned. Now when the car is started cold, the idle sticks at 1400 no matter whether I drive it 5 miles or 100 miles. BUT if I shut off the engine and restart it hot, the idle is fine. I don't even have to stop the car and crank it to start -- just turn off the key for a couple seconds while driving, turn it back on, and when I stop at the next intersection the idle is perfect. Replaced the IACV with a known good one, and it still acts exactly the same. So the problem likely is somewhere else, but where?

redyute

iTrader: (2)

Does she throw any codes?

r berq

Not sure. The check-engine light is not on.

Former User

Does the CEL work?

r berq

Yes, CEL works. I have turned it on multiple times by disconnecting various sensors.

r berq

It acts as if the computer reads coolant temperature when the ignition switch is first turned on, and never reads it again. So it maintains a stable idle based on engine temperature at startup, whether it be hot or cold, and doesn't adjust it no matter how long the engine runs or how much it warms up. Even if the car is sitting in the dooryard, and temperature in the top of the radiator is 210 degrees, the idle does not drop if it was started cold.

delsolintegra

I had to replace the coolant temp sensor in my 98 Integra RS because my temp gauge was always reading too cold even after warmup.
I think that sensor can deteriorate over time and not give the proper temp signal to the temp gauge and maybe the ECU also ?

r berq

Good thinking. I hoped that might be the problem, but I have checked the sensor from 195 degrees all the way down to room temperature (as the engine cooled off) and it is very accurate according to the chart in the shop manual.

r berq

Problem with the fast idle turned out to be a mis-adjusted TPS. It was set at too high a voltage, so the computer never saw the throttle as closed, therefore the computer didn't adjust the idle.