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Discussion Starter · #1 ·
I seem to be having idle problems with my z6, it seems to hunt from 1500 to 2500 rpm and I have pretty much changed everything possible and checked for vacuum leaks and there is none. I have a chipped p28 and there is no codes except a code 20 (electronic load detector) but being a uk car it doesn't have one???

When I turn the ELD off in the tune the car just refuses to idle anymore unless I turn the ELD back on. Genuinely have no clue what to check anymore.

If anyone knows anything that might help it'd be greatly appreciated.
 

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93 4d lx, z6,ported, port matched, compression bumped, balanced, manual swap
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Where is slo with that gif?
Start with basics, check for slack on cable, verify tb closes all the way, burp the coolant system, then pull the idle screw out, inspect the oring, replace if needed, reinstall, gently seat, back out 1.5 turns, start the car and bring it to operating temp, shut it down, unplug the iacv, adjust idle screw to 650-750 base idle, shut the car down, plug in the iacv, restart and check idle. Still not right? Check timing(ignition and mechanical), check tps and ect sensors. Still not right? Plug in a stock p28 and see if it idles closer to right. And lastly, check your alternator for a set of torched bearings or a bad regulator diode pack, not common but ive seen it cause an eld code and rough or no idle.
 

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That isnt the correct IACV and idle adjustment. WIth IACV unplugged, you adjust idle to 450-500 rpms, but that assumes everything else is PERFECT. An idle adjustment is useless with a fault or issue.


Ytaq, remove the air intake tube from the throttlebody, and cover the throttlebody with a block of wood or something sturdy enough to not get sucked in.


If the engine does NOT stall, you have a large vacuum leak, plain and simple.


If it stalls out, unplug the IACV, stick your finger over the IACV air port in front of the throttle blade, and fire the engine up with a friend in the driver seat. Make sure to tell them to LEAVE THE GODDAMN THROTTLE PEDAL LONE with your finger in there!! Disconenct the throttle cable form the butterfly spool pulley if you get worried.

With the IACV port blocked off, you should be able to idle around 450-650, depending on how much air is getting through the idle screw port.


Post updates when you can.


Sometimes a good amount of carb cleaner sprayed into the throttlebody while it is idling high will clean the proper passages, then you shut the engine off after a few seconds, and yank the battery negative for 10 minutes, or you can simply hop into the driver seat, and press the brake pedal to drain a bit of power while using the key to attempt to start it. This should drain any remaining power quickly, rather than having to wait 10 minutes.


Then reconnect the negative cable and fire the engine back up. See if cleaning it solves it.
 

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Discussion Starter · #4 ·
Hey guys!

Thanks for the suggestions, I'll get to trying all these out when I get some time off work.

I do also have a new map sensor on the way so I'll check to see if that changed anything when it gets here.
 

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93 4d lx, z6,ported, port matched, compression bumped, balanced, manual swap
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My 650-750 rpm recommendation assumed he had a bit of work done, and will generally get a mild to medium modified engine to idle around 900 or so, maybe I should have verified mods first, but why tune a p28 for anything less than mild internal or head mods?
 

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Hey guys!

Thanks for the suggestions, I'll get to trying all these out when I get some time off work.

I do also have a new map sensor on the way so I'll check to see if that changed anything when it gets here.
what data did you check to see if it needed a MAP sensor?

Throwing parts at it is not diagnosis.

What if it ends up being a simple clamp that fell off the brake booster and the leak is muffled from being right on the fitting?
 

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93 Civic Cx hatch
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I know not everyone's experiences align but when I got my mini-me done I had the exact same thing happening. My idle was between 1500-2800 but for the most part the higher end of that. I tried many of the things people in here have said already and nothing would fix it.

What fixed it for me was I ended up backing out the screw that is underneath where the throttle cable connects. I believe it is called the throttle stop screw. I backed this thing down an obscene amount, 2 or 3 mm. It even appeared to be in the stock position initially because the paint mark was lined up still. After doing that my idle was at right around 800 and I was happy there. Been that way for a while now with no idle issue coming back. This is like the end of the rope nothing else has fixed it type of fix imo but it is an option if you cannot find anything else and may be worth trying rather than throwing parts at it.

This is a picture from a DIY on something else not fully related that I found that should help you find it.

throttlestopscrew.png
 

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93 4d lx, z6,ported, port matched, compression bumped, balanced, manual swap
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If the tb is from a different setup, mostly the crv b20 I think, I've had that issue as well, but you still gotta do the base work and eliminate other potential more common causes first, I've had knuckle heads back that out entirely and cause no run issues that left strings of shops scratching their heads.
 

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damnit, too old to find my old post about resetting the thermo whatever under the TB that backs out under engine vibrations..

Don't fuck with the throttle stop, leave the 7mm nut alone unless Gude has touched your throttle body!
 

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Bone, you talking about the FITV? Basically just needs a disassembly, cleaning, hand snug back together, back off 1-2 turns I think, or leave it slightly snugged, I forget.

Those can be a bitch to pull off, those goddamn tiny screws!!
 

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93 Civic HB SI
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Yeah, adjusting the throttle stop is not recommended. Many reasons why.

That thing is set to place the throttle blade to prevent blade sticking, bore wear, as well as having a very VERY small predetermined amount of allowable bleed air to pass the blade at a low volume/high velocity to reduce throttle snap plenum turbulence. Having a tiny amount of bleed air allows a smoother flow of air into the plenum between close and open throttle. Instead of a tightly sealed dam holding back a wall of air that just dumps abruptly into the plenum in an uncontrolled manner, having a small amount of bleed air allows smoother air flow characteristics into the plenum when the throttle blade opens. The rest of the air coming in tends to follow the direction of the air already bleeding in, and allows more predictable and controllable air flow into the plenum.

Another good reason that gap exists, is high velocity air at the blade to body gap helps to keep the gap clean, and that tiny amount of bleed air moving moves oil mist/droplets and carbon build up along.

Daily drivers with enough mileage end up having carbon build up that reduces or seals this gap. Usually, most people don't even notice, but for those who are well in touch with their cars, it is usually a noticible difference between a dirty vs clean throttle body. Response of the engine seems snappier on a clean TB, air flow characteristics into the plenum have improved since you've cleaned the gap allowing the bleed air to pass.

Throttle stop settings from Honda are a precision adjustment done at the TB manufacturer and should not be altered.

If idle is high and not being controlled correctly, that screw is NOT the reason unless it's been previously f***** with!
 

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'93 / '95 Del Sol Si - '95 DX Coupe - '00 Accord EX F23 Manual
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Here is the question - When was the idle correct? Was it ever correct? And what did you do to the motor before the idle decided to go rogue on you? Was anything done to the car before this happened? Or did it really just mysteriously happen?

I've had Hondas idle fine for years. For a decade. I've never had idle problems that I didn't ask for by swapping something or changing something. And 99% of the time, it's the IACV.

For example - If I put in a Skunk2 intake mani, I have to back the IACV off 15-20%. Or else it just idles high and hunts. On every motor I've ever thrown one on.
 
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