Hey guys, I'm new here. I just posted in the Introduction forum if you want to know a bit about me.
I currently have an idle issue that I did not have before.
The car is a 94 Del Sol with a boosted D16Z6
When I bought the car, it had a externally leaking head gasket, but would idle at 1500 rpms when cold, and would settle down to a steady 850 after warmed up. It ran decent, but I wanted to fix the leak before it got worse.
I replaced the head gasket, had the head resurfaced, new valve stem seals, new intake and exhaust manifold gaskets, new vacuum lines with a SickSpeed vacuum manifold, new (IAC) Idle Air Control Valve, replaced a bad injector with a good used one, new injector o-rings, and a bunch of cleanup.
I have a chipped (previous owner had it tuned) P72, and a AEM AFR gauge.
I start it up cold, and it idles around 1500 rpms, and after it warms up, it idles over 2000 rpms. It runs strong under load, and pulls nicely. The only new mods after the tune were going from a open downpipe to full 3" exhaust with a Megan Racing muffler without a silencer, the new IAC, and I replaced the IAT sensor with one from a junkyard (and repaired the harness). It had a code 10 when I bought it.

There are no CEL codes, and it runs well other than the really high idle.
The AFR gauge show around 17 at idle when warmed up (14.7 when cold). Under load it drops down to around 10.
I am new to the turbo scene, and unsure what that means. I think the 17 at idle means super lean (I heard at idle, that may be ok).

The other possibility is that I was dumb and forgot to disconnect the battery (in the trunk - out of sight - out of mind) and when I was putting in the transmission, I grounded out the 12V starter wire. Is it possible that I messed up the tune? I would think it would run poorly if that was the case.
I opened up the ECU to verify the chip, and did not notice any damage to any of the capacitors or anything.

I am going to check for any vacuum leaks around the TB and Intake with some brake cleaner, but I didn't touch the TB, and the intake gasket is new, and torqued to the right specs.
I am also going to check my valve clearance.

I currently have the idle screw bottomed out. The throttle cable has a good amount of slack.

So, does it sound like I messed up the tune by grounding the 12v?
Should I take it to a tuner (will they be able to help)?
Should I investigate further, and if so, what should I check?
I am electronically inclined, and not afraid of a soldering gun or a multimeter.
Thanks in advance!

 

Get some stater fluid and spray around the injectors and all the gaskets. Odds are you have a vacuum leak somewhere, the car will have a change in tone once or if you hit the leak

 

also check the connector to the idle control valve and the intake air temp sensor. They are very similar but it does sound like a vacuum leak is present. I would inspection the sick speed manifold box also. I have had issues with them myself but not that particular brand.

 

@turboLScrx I'll spray some stuff once I get it back together if the issue persists.

@roddrick The connectors are tight and clean. I am sure that the IAT connector is the right one. The idle issue was there before the manifold box was added. I just wanted to have one source of vacuum for consistency.

I checked some things yesterday, and "may" have found the issue(s)?
2 things stand out.
I read other places that the FITV plastic screw can come loose and mess with the idle. I found that the plastic screw was completely unthreaded so I re-seated it.


I pulled the throttle body off to replace the gasket for sanity and I saw that the new IAC valve only had one coolant line going to it. I read that it can cause other idle issues.



Only 1 hose connected to new IAC

Back of head / intake manifold. B went to B on the TB. I have one capped off that I could use to hook up the IAC lines?

I am not sure how to hook up the coolant lines around the TB / IAC. I do not have the coolant pipe behind the motor since the engine bay had everything removed that wasn't needed.
Any guidance on hooking up those coolant lines?

 

FITV could definitely be the cause. I personally delete the FITV on all my setups now - the IACV can handle all the idle control function on its own, and keeping the FITV is just another potential failure point. Honda was experimenting with idle control on these engines and on some they employed 3 different idle control mechanisms on the same engine. You can get a nice machined block-off plate on eBay for about $20.

Since you're in FL, I would say just delete the IACV coolant lines. They have no impact on how the car runs in warm climates. It's only to keep the valve from freezing in sub-zero weather.

 

Interesting. I didn't know deleting the FITV was an option. I think I'll try cleaning it, and see if the idle goes back to normal, and if there are still issues, I'll get the block-off plate. They look nice.
Wow, that's crazy. Yeah, it seemed overcomplicated.
So, if I keep the FITV, do I just cap off the other coolant lines for the IACV and the TB?
Do I keep the wiring harness connected to the IACV?

 

If you keep the FITV, it is a good idea to attach a coolant line to it. The way the FITV operates is that as the engine heats up, the coolant flowing through the FITV heats up a wax plug, causing the wax to expand and it closes off the valve. It's a purely mechanical valve. Until the engine is hot, the FITV basically operates as a vacuum leak, allowing air to bypass the throttle plate. If you don't give the FITV coolant, it will take much longer for the idle to come down to normal, as then you are relying on the heat soak of the intake manifold/throttle body/FITV to cause the wax to expand.

On the other hand, the IACV doesn't need coolant to operate - the coolant lines are only there to help the valve not stick in sub-zero temperatures. It's a solenoid that receives a PWM signal from the ECU to tell it how far to open. So yes, you can just cap off the coolant sources that would go to the TB / IACV and leave the ports open on the TB and IACV if you want, or you can cap them. It won't matter either way.

Do you have the ability to edit the chip in your ECU? It may be beneficial to adjust the IACV duty cycle slightly if you do decide to delete the FITV. If you don't have that ability, I don't think it will be a big deal, as the ECU can "learn" how to idle on it's own to some degree.

Here are some pictures of some mods I did to my Z6 IM/TB before I switched to a Skunk2 Pro:


Here is the block-off plate installed. I just cut off the nipple where the coolant hose went into the TB to clean up the look since I wasn't using it anymore. I just removed the lower portion of the IACV (not pictured) where the coolant ports attached.



You can probably get away with just using a rubber cap, but I cut off the coolant nipple here where the small coolant line came from, tapped it, and threaded in an bolt with Permatex Ultra Grey on the threads - never had an issue with it like this. I also modified the water pipe on my block to have the small nipple there welded shut. Again, a cap of some sort would be fine.

 

Awesome! Thank you for the detailed explanation on how those parts operate.
I don't have the equipment to alter the chip. I plan on getting it dyno tuned once I get all the kinks worked out. I'll ask the tuner to make any neccessary adjustments to the IACV when I get it tuned.
Thanks for the ideas too with the pictures. I'll update here once I have it back together.

 

This thread is in the wrong forum. normally I'd move it over to the correct one, but I don't want to spoil the good influx of information brought on by others. It's good to see people being so helpful again.
So, pauleatstoomuch, welcome to H-T, I'm really glad you're getting the feedback you're looking for. Just for future reference, however, please ensure that your thread topic is in the correct forum. I know there are a lot of forums to choose from, and it can sometimes be difficult to decide as to which one is best relevant for your topic, but just keep an eye out, k?

In the meantime, carry on...

 

and the grinch’s heart grew 3 sizes bigger