'96 Civic (High) idle issue

Mr.Baker

Mr. Search
Registered VIP
5+ Year Member
10+ Year Member
I usually am good and researching and trouble shooting, so I thought I was on the right track with it being a faulty IACV.
But I also see so many different answers, so I'm second guessing myself.

'96 Civic Dx, auto, 170k on the d16y7.
CEL is on, I assumed it was for infamous cracked exhaust manifold faulting the o2 sensor.
When I first start it, it idles fine.
On warm days, 75+, the idle wants to take off the warmer the car gets.
I once left me car on, its's about 80 out and I went into a store for less than 5 mins, I come back out, it's "idling" at almost 4k!

High idle is usually vacuum leak related?
It not doing this when it is cooler out so is it temp related?
First I thought it was the IACV, reading about it being coolant related.
Now after reading more into this, I feel like I am chasing my tail and the answer is not so obvious, making me feel like a total honda noob..ugh!
 
Last edited:

Mr.Baker

Mr. Search
Registered VIP
5+ Year Member
10+ Year Member
I've let this sit awhile out there, still trouble shooting, tried the low coolant thing, and it still want to do the same thing. Still stumped, any ideas?
 


lethal6

Your Mom's Moderator
Staff member
Registered VIP
Registered OG
5+ Year Member
10+ Year Member
You said that the CEL is on and are assuming it is for faulty O2. Did you scan it? What code is it? I know most people don't even look that route, but the codes can lead directly to what is going on. It's the main reason they are there, to save time for the technicians so they don't have the "chase their tales" like you are having to do right now.

Also, did I read that right...you left your car running unattended while going into a store? Someone was in the car watching it right? People still do that? In my youth, I was a terrible teenager and used to love people that left their cars running at stores or in the morning to warm them up. It was like free candy to us. Never used to destroy the cars or vandalize them in any way, we would just use them to get where we needed to go and dump them in a parking lot somewhere when done. I have since paid my dues (in various ways) but I am definite that there are kids that still do that. /pointless story :lol:
 

Mr.Baker

Mr. Search
Registered VIP
5+ Year Member
10+ Year Member
You said that the CEL is on and are assuming it is for faulty O2. Did you scan it? What code is it? I know most people don't even look that route, but the codes can lead directly to what is going on. It's the main reason they are there, to save time for the technicians so they don't have the "chase their tales" like you are having to do right now.

Also, did I read that right...you left your car running unattended while going into a store? Someone was in the car watching it right?
The cel showed up after the manifold crack made it all the way through. But no, I should have it scanned and not assume. This idle issue reared it's ugly head before the cel came on, which is also why I assumed it was not related.

As for leaving it unattended, I have no worries about it, the would be joy riders, would bring it back the minute they put it in gear and.... it's not that type of area.
 


Joe Mason

Respected
Registered VIP
Following. One piece I'd check would be the throttle cable adjustment. If possible, take it off the bracket, just to rule out that it's not borking things up.
 

Mr.Baker

Mr. Search
Registered VIP
5+ Year Member
10+ Year Member
Following. One piece I'd check would be the throttle cable adjustment. If possible, take it off the bracket, just to rule out that it's not borking things up.
I can't believe it would be since it seems temp related.

One other thing I have noticed is, once it goes wild with the idle, I get it on the open road and throttle it, when I come to another stop, it's kicked back down to normal.
 

Joe Mason

Respected
Registered VIP
Another possibility could be the TP sensor going bad.

I've let this sit awhile out there, still trouble shooting, tried the low coolant thing, and it still want to do the same thing. Still stumped, any ideas?
What's this low coolant thing you speak of? Draining some coolant to see if it affects idle?
 

bairdandrew77

New Member
My best guess would be vacuum leak. One of my cars would idle fine on colder starts but would hunt between 2.5k and 500 rpms. Turns out the wrong TB gasket was installed leaving a massive hidden air leak.

Could also be the iacv but I never heard of it causing revs to go up to 4k..

Is the idle fluctuating or staying steady? Either way I'd check for vacuum leaks first. Carb cleaner method or if you can find a smoke machine to borrow that'll be much better.

Sent from my SGH-T399 using Tapatalk
 

2nd_gen

TURD-BO
5+ Year Member
10+ Year Member
15+ Year Member
First I thought it was the IACV, then reading about it being coolant related.
iacv IS coolant related.

take it out. clean it good. reinstall then let us know what happens.
its simple, its free
 

Mr.Baker

Mr. Search
Registered VIP
5+ Year Member
10+ Year Member
iacv IS coolant related.

take it out. clean it good. reinstall then let us know what happens.
its simple, its free
I know IACV is coolant related, typo on my part.
But I did clean it, no change. Which is leading me towards vacuum leak...
 

Mr.Baker

Mr. Search
Registered VIP
5+ Year Member
10+ Year Member
Update.

Finally replaced the cracked exhaust manifold and replaced both o2 sensors.
Codes cleared and now I think I have it figured out.
I can hear a high pitched whistling, changes with throttle position, thinking now its's intake manifold gasket leak.
Right now, it's getting cooler with the changing seasons and the high idle issue isn't an issue in the winter.
 


Top