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Like the title says, I have a strange hunting idle problem on my 97 Honda civic LX 1.6L 5 speed.

The story, I test drove the car for a couple minutes, nothing seemed wrong. After I bought it, I noticed a hunting idle between 1k and 2k, After 10 minutes perhaps.

The things I've done: removed and tested IACV. Wasn't clogged but I sprayed with brake cleaner. I tested it with 12v, it opened one way, closed the other with no sticking so I assume it's fine.

Also before that, I replaced TPS due to low current engine code.

And I removed MAP sensor and verified resistance was within the correct bounds (I think it was 2k ohms) and changed when I applied mouth vacuum.

So now, the actual issue: I start up, everything looks normal besides usually idling at 1.2k rpm. After it warms up, when I press clutch or shift to neutral, idle goes down to 1k, then rises to 2k, then plummets to 1k.

Another thing, I seem to have to give it a lot of gas for it not to feel like I'm lugging engine. I sometimes rev to over 2k before I let out clutch to try not to do this, but I don't always succeed.


Now one thing to note, my IACV looked very different than the one I found a guide for cleaning it. Maybe it was for a different year/engine? Also MAP sensor looks like non OEM. And by removing a connector to the MAP or temp sensor on the air box, it sometimes can make idle stop hunting.


Now here's the real puzzler for me. Several times while my engine surged from 1k to 2K rpm, I slammed on the gas, and immediately let off, (up to 3.5k?) and the idle went to a near stall! Steady at the little mark on the tach . (It looks like 100rpm or less on guage) this has happened several times, but not every time I've tried it.

And a couple times it was starting up cold and nearly stalling (one day it actually did stall, had to press gas to keep it running).

I probably missed some things cause it's pretty late, but I wanted to get this up to get feedback.

I'm thinking of buying throttle body for fifty bucks at junk yard, but would much rather find the root of the problem.

Thank you anyone who reads this and especially anybody who replies,
Matt

 
Rep Power: 174

Hmm, maybe the injectors are dirty...

 
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If that's the case is there an easy way to do a test?

Also wouldn't I be having other signs of trouble while in gear?

I forgot to say it has 151,000 miles.

 
Rep Power: 174

Where did you find the guide for cleaning the IACV? If it was here, it was probably by gearbox and he has a 2002 I believe.
I found some info here
and with Scotty Kilmer (my favorite)
Do you ever run any additives in your fuel? Some people swear by Techron. I use LubeControl myself.

 
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No I never used additives but only owned car for about a month.

Anyway, New info. Previously I had engines code red at advance auto parts. I noted them, pulled the fuse and battery, reset computer then had codes read a week or so later. Just TPS sensor low input,so I replace it. Reset computer, and I just read the codes again and all are back.

TPS low input
MAP sensor
RACV circuit error (Previously idle control failure or something)
IAT sensor high input

So I'm going to check local salvage yard for sensors tomorrow. Anybody know why the codes would come and go like that?

I guess I will also check iacv, but I don't see why it would report that error.

After I replace MAP, IAT, and verify TPS has correct volts, I'll give another update.

Thanks!

 
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I found a IAT and MAP sensor at junk yard.

I put them in, verified TPS had correct volts.
It was a hair over 0.5V closed, and a hair over 4.5V wide open so I don't understand why it would throw a code. Also checked IACV leads for continuity (meter beep mode) and pretty much there was continuity everywhere. Middle to each side, side to side.

Now I drove several miles and heat gauge was near middle (was warmed up going to junk yard prior).
I pulled over, turned off key, pulled out HAZARD 10A fuse, waited 60s and put it back in. Then started and let idle with no acc on, no pedals pressed for a good 11 minutes. Turned engine off, then started and went back home.

I saw slight improvement, however the issue varies from time to time so it could go back to being severe idle hunt soon, I don't know.

One thing though, my o-ring for map sensor was cracked. Luckily I took one off the junk yard car. Swapped it out before I did the idle relearn, and was really really wanting that to be the problem. So much for that.

After I got home in my parking space I again stepped on throttle, immediately letting go, and I could get rpms to go very very low.

At this point I tried putting on headlights and heater, and my engine did not dip down rpms like it uses to, so maybe that's something.

Anyway next time I go out I'll try to take a video of my cluster and post a link, so you guys can see my needle bouncing around. Meanwhile I'm still open to suggestions.

 
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Good news, guys. I have appeared to fix the problem! I say appeared, because I took it on a short drive, and had no idling issues at all! [It idled about 1K, but I have not done an idle relearn since fixing it]

What did I do? First I got a IACV from a junkyard car. The guy at the place grudgingly let me take it off the throttle body [because another employee told me I could take one off]. I paid them $15 for it, and on the way home, bought some carburetor cleaner [I only could find brake cleaner at home].

I removed the whole throttle body, because I was sick of the problem, and wanted to rule out the throttle body was clogged. I sprayed it, let it sink in, wiped it with a rag, and a screwdriver with rag wrapped on the end, scraping gunk off in hard to reach area.

Next I cleaned the junkyard IACV, since it actually looked dirtier than my current one, with the coolant plugs actually rusty, while mine was nice and shiny.

Then I wiped the gasket a little bit, since there was some black build up [nothing too bad].

Then, I put everything back together, and to my amazement, there my car was, idling at 1K after a short trip! I was elated.

tldr;
I replaced my IACV from one I took off a junk-engine civic at the junk yard, removed and cleaned both IACV and throttle body, and put everything back together, and my problem seems to be gone!


I will also add, I had tested my IACV with a variable voltage DC power supply, and the solenoid seemed to function correctly. I guess you really can never tell, if it's $15, just throw a different IACV on, and you might just fix your whole problem.