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93 maybe 94 coupe
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289 Posts
Discussion Starter #1
So as the title says, fitv blockoff was leaking, had been driving on it for a week or so, now the car dies approaching stoplights unless I catch it w my foot when the revs are dropping out of gear, then it idles fine.

No cels, no vac leaks, didn't reset the ecu

Can someone help me understand what's occurring? Not asking for a fix, just understanding.

Car ran great pre leak, idled high w the hiss, no other changes

No surging, car has good power and drivability otherwise.

Thanks in advance for your time guys
 

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BATSLOMAN GIVES NO FUCKS.
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4,099 Posts
it was letting enough air to bleed by and compensated.
 

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Registered
93 maybe 94 coupe
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289 Posts
Discussion Starter #3
So ill reset my ecu. I've only driven it twice, maybe 5 miles....died reliably lol
 

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93 maybe 94 coupe
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289 Posts
Discussion Starter #4
Reset ecu, no change. Unplugged iacv hot car wouldn't idle. Shimmed the idle screw temporarily til it would idle without iacv, plugerred it back in and it idled high w cel, cleared cel/reset ecu now it idles great hot but idles high while warming up after normal cold startup. Idle sits at 900 on catalog.

Datalog also indicates tps is at 7% at idle and the idle still dips before stabilizing when coming to a stop. Revs also drop more slowly than normal reinforcing that. Dunno what tps says unshimmed, probably shoulda made note of that.

I'm thinking the throttle might be crutched open too far for iacv to dig it and I gotta make it idle on the stock idle screw position. (Currently 2 layers of gorilla tape acting as shim)
 

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93 maybe 94 coupe
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289 Posts
Discussion Starter #5
Starting to question the functionality of my iacv
 

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Reset ecu, no change. Unplugged iacv hot car wouldn't idle. Shimmed the idle screw temporarily til it would idle without iacv, plugerred it back in and it idled high w cel, cleared cel/reset ecu now it idles great hot but idles high while warming up after normal cold startup. Idle sits at 900 on catalog.

Datalog also indicates tps is at 7% at idle and the idle still dips before stabilizing when coming to a stop. Revs also drop more slowly than normal reinforcing that. Dunno what tps says unshimmed, probably shoulda made note of that.

I'm thinking the throttle might be crutched open too far for iacv to dig it and I gotta make it idle on the stock idle screw position. (Currently 2 layers of gorilla tape acting as shim)
Ok stop.

First off your IACV sounds fine. Idling high after a cold startup is how cars are supposed to function.

Second your throttlebody has an idle screw, which is basically a controlled vaccuum leak, you dont have to gerry rig the throttle, dong that is messing up everything else.

Turn off all electronics, remove crap holding open throttle, let the car warm to normal operating temp, unplug the IACV while the car is idling and adjust the throttle bleed screw until it is idling around 450 RPMS, dont mess with anything that moves the throttle plate. Once the car is idling around 450, turn it off, plug in the IACV, reset the computer and you should be done.
 

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Meat Popsicle
91 CRX Si
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2,936 Posts
OP said he reset the ECU and unplugged the IACV and it still wouldn’t idle.

I was running a JRSC A6 setup for years with the S-tube plumbed to the black box and a breather on the valve cover. Car idled fine.

I capped off the port on the s-tube, which was essentially just pulling in air through the crankcase and causing a big vacuum leak, and the car would not idle.

Long story short, I swapped the IACV and was then able to run with the S-tube port capped.

With the vacuum leak, the IACV was able to open enough to let the car idle. When it was capped, it wouldn’t open far enough to let it idle.

My theory is that if you’ve been running with a vacuum leak long enough, the IACV can get “stuck” in a limited range of motion. Once the leak is fixed, it can’t open enough to idle correctly.

You may be able to clean it by spraying TB cleaner in it but that might also screw it up
 

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Classic Man
Civic
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16,355 Posts
Chances are the TB and the IACV are dirty, their flow has been reduced.... the vacuum leak made it so it wouldnt stall at low RPM.

Clean TB with carbon cleaner around the TB blade, flush the idle air port, pull IACV and flush IACV port and flush IACV. Bet she runs like a champ after.
 

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93 maybe 94 coupe
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289 Posts
Discussion Starter #10
Ok, some great discussion here and I'll update when I get to flushing stuff out but first some clarifying.

It wasn't idling high as in normal operation. It was hanging higher than that and didn't react as though the throttle was closed 100% between gears as is usual operation.

A near normal idle speed was achieved only after 25-30 minutes of driving w ECT reading 189 degrees w fans cycling several times.

Our other civic idles and starts 100% normally acts well, as one would expect. Please see my NEW post about the problem on that one that emerged recently lol
 

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Dont forget to unscrew the idle adjuster screw out completely, and make sure that o-ring on the end is clean and not torn. That will allow a leak regardless of position. I like yanking it, spraying with brake cleaner, install all the way tight, back off 2 full turns, and test form there.



Stole image from hondatech via google
 

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93 maybe 94 coupe
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289 Posts
Discussion Starter #12
So i take it that is like the idle bleeds on a weber? Ok to adjust this, but not throttle stop, correct?
 

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throttle stop has a specific adjustment per manual.

idle screw has a specific rpm you are supposed to shoot for during adjustment, per manual.

search on google "ab0ve civic manual". that is a zero in "ab0ve"

Find a few hours of the day or week, and crack on. Lots of good information that even translates as a generic diagnostic response to any vehicle conditions, or at least gives you one more thing to try out.
 
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