First of all, I know a lot of people like to say to go read what’s already been posted but honestly, I’m not finding much specific to my issue. I’m completely new to this forum and honestly any forums. I’ve seen a lot of useful information on here and a lot of very knowledgeable people so I’m hoping to get pointed in the right direction here.

3 months ago, I imported a 1991 FC3S GT-R (obviously turbo). It ran great! No issues at all. The intake was an aftermarket mushroom style filter that was crumbling through and bound to be an issue so among all the basic maintenance, I swapped this to an APEXi Power Intake. Cool. Not sure how relevant this is, but it didn’t seem to be a perfect fit, so not sure if this is letting in unmetered air or whatever, but after install it ran fine multiple times. Fast forward a week or 2 later, I have to drop it off with a body shop which it was ultimately there for 2 ? weeks. During this time, it got cold as hell and quick. To my knowledge, it’s still on the stock ECU and nothing else was touched at this point. When I got it back from the body shop, it was unable to hold an idle on cold start unless I applied gas manually. After a few minutes of this, I could let off and it would idle comfortably around 1k rpm, not much surging or anything like that. I assumed it just didn’t like the temperature change and I kept it pushing.

With all of this being said, the car runs and drives GREAT when it warms up. No loss of power, throttle is responsive, turbo spools up great, doesn’t SOUND like there is a leak on the intake.

Now, it’s seeming like it’s gotten worse. Granted, at this point I’ve upgraded to a full turbo-back exhaust, catless downpipe, midpipe, catback. Now, the same issue occurs with needing gas to idle, but now even when it warms up if I let off to let it idle by itself it is a very low idle and seems almost like it wants to stall out, very choppy but the surge is nothing crazy it just stays extremely low.

I know I need a tune to properly run on US fuel and a new exhaust, specifically catless. For the most part, I haven’t driven the car much because of this and I’ve tried to stay out of boost when I did drive it (emphasize on *tried*, because we all know I hit boost a few times)

At this point, I haven’t tried much. I’m new to rx7s and what I keep seeing is calibrate the TPS but wouldn’t this affect drivability completely, not just the idle? I’ve also read about IACV and BAC to clean them out, I just don’t know where to start knowing I don’t want to run the car too much until it’s tuned but I’m not sure I can take it to get tuned until I’ve resolved this issue.

Any help or information would be greatly appreciated. Again I’m sorry if this answer is posted elsewhere, but it seems like most of these posts don’t really apply to my situation. I’m stuck between it being cold, it sitting for a while, weak battery, IACV or BAC, vacuum leak which I don’t think so considering everything else is fine. I do have a compression tester. I ordered new plugs assuming I might’ve fouled these ones driving rich/lean. I have a new ECU waiting for tune time to be installed.

Maybe I’m completely ignorant to how all of this works and missing something extremely simple. Also like I said I haven’t tried much. Sincerest apologies if this is the case. Hopefully one of you rotary wizards can help a brother out here…

Would also like to add it cranks and starts no hesitation, literally every single time. Starts right up, does the normal rev up to 2-2.5k rpm, drops back to where it belongs, then slowly falls out and dies. When it drops back down is when I’d start to give it gas.

 

If you're still on the stock ECU then this could be two things:

- The thermowax on the throttle body is clogged (or has been removed, since people like to do that). This is a little wax pellet that bumps the throttle blades open when the engine is cold, so if it's not working then when the engine is cold it might not be getting enough air.

- Less likely is that the temperature sensor on the back of the water pump housing is bad / unplugged. If the ECU doesn't see this reading then it assumes the engine is warm and there is no cold-start enrichment.

You can read how to check / fix both of those in the factory service manuals available at Foxed.ca.

 

Your current issue is almost identical to mine. Except mine is an N/A. I am assuming it is my primary fuel injector seals.
Check your secondaries first. If you push on the injector(s) and it spins or moves, the seal is probably leaking. I am not sure how to check to certain it's leaking or just loose.
The primary's would need to be accessed after taking off the upper intake/throttle body, of I am not mistaken.
Maybe someone else has some ideas. I would like to know as well.

 

Thank you for the response.. if you don’t mind me asking, why would somebody remove this? I couldn’t imagine any power gains or anything?

I guess if they aren’t in cold temperatures, but Japan gets pretty cold.. atleast so I’ve heard. Doesn’t seem very logical.

Again thanks for the idea. I’ll research this a bit and see what I can find. Thermowax is a new one for me.. from all the forums I’ve searched I don’t think I’ve seen this mentioned lol

 

Correct me if I’m wrong, but wouldn’t an injector seal leak result in hard starts even when warm? She cranks and starts right up every single time, it’s just been the idle

 

There aren't any power gains.

People used to be really obsessed with removing emissions components on this car to "clean up" the intake. EGR, vacuum solenoids, air pump and control valve, thermowax, secondary throttle diaphragm, even the aux port actuators on NA cars.

The trouble is that almost all of these components are also for drivability. Particularly on the stock ECU which is tuned around having them there.

I'm not sure why this was the case. I suspect it's the usual case of a track focused mod making its way to street cars, and new owners looking for free mods with the idea they can gain some HP.

Nowadays it seems to be commonly accepted that removing these parts is pointless and detrimental for a street car, but for a long time it was popular. Every so often new owners still post looking for help with their idle and then they upload a picture of the engine bay and half the parts are missing.

 

Gotcha, thanks for the information. I would have to agree that this would be pointless and detrimental.

So here’s my question; In your opinion, is it worth me going out there and pulling off the throttle body to inspect thermowax and BAC, or is this something the tune would be able to essentially “bypass”, or atleast resolve? I wouldn’t mind holding off on it until the tune if that’s the case, since it’s still not tuned for 93. The ECU I have is an APEXi Power FC. I’ve been hesitant on bringing it for a tune with this idle issue but from what I’m gathering, it wouldn’t necessarily matter would it?

 

My original comment was based on the assumption you still had the stock ECU (which I think you said you did in your initial post). I don't know a ton about the PFC but I'm pretty sure you don't need a thermowax with it since it can control the idle valve and just use that for warmup. In fact, installing an aftermarket ECU is one of the good reasons to remove the thermowax (since the ECU can control idle now).

Do you have any way to pull the logs from the ECU? I think for the PFC you need a special box that would allow you to connect it to a laptop for tuning / logging, but again I have no personal experience with that particular ECU. If you can pull logs then it might be easier to diagnose the issue.

 

yes, its an old car, you need to basically verify everything to make sure its a, there and b works
also its an FC, so its probably been apart a few times, and who knows what the people before you did

 

Sorry for the confusion. The car is running on the stock ECU currently. I have a Power FC in my possession which was what I planned on installing for the tune.

Since it can control the idle, and thermowax would be out of the equation, is there anything else worth checking before bringing it for a tune? Probably just clean and make sure BAC is working properly?

I just wanna make sure I’m not doing any damage running the car as it is now, and also that when I bring it for a tune there won’t be an unexpected surprise on this idle issue that won’t be able to be controlled via PFC

 

Sorry, I didn't see this before I responded.

 

Yeah, this seems correct. I found that you can spray stating fluid near the primary's while running and it will change idle if they are bad.

I was referring to this part.... not the no idle while cold.
If you solve for this with the stock ECU, let us know. I have the same issue. Now that the injector idea is out, I am stuck because as far as I know as the thermowax is disabled after a warm up. Yours could be as simple as another TPS adjust, perhaps mine too.

As far as what to keep and what to pull out.... I assume that the person that you will take it to for a tune with the new ECU will be the best to ask. It could be easier or more familiar territory for them one way or the other.

As a side note j9fd3s and WonderousBread are both incredibly knowledgeable with 7's unlike me. You are in great hands with those two....best wishes!!

 

Honestly, I’m assuming my rough idle has more to do with fueling since it’s still tuned for JDM fuel and I removed the cats for the new exhaust. Could be wrong, but atleast in my situation it didn’t start doing that until the exhaust install. And yes, from what I understand, thermowax is purely for cold starts.

Hate to recycle the same basic junk at you but for a rough idle in normal circumstances, all I’ve seen is to clean the BAC/IACV and confirm functionality, check for any intake / vacuum leaks, and adjust the TPS. But my knowledge is extremely limited.

And yeah haha I’ve seen them on a few forums on here, definitely some of the “rotary wizards” I mentioned before. It’s pretty cool to know there’s still people like that out on these forums lol

Anyway, I’ll probably swap in the new ECU and bypass the thermowax, so as for solving on the stock ECU I may not be the one to resolve this (unfortunately)

Thank you for taking time out of your day to respond, even if you didn’t have an instant answer for it. Any and all help is appreciated. Best of luck to you as well brother

 

Thinking about what Jeff said about the injector seals, it might be a good idea to check those (and everywhere else) for vacuum leaks. It's possible that something is not sealing when it's cold because it's contracted, and then when the heat expands it it tends to plump up a bit. Or it's also possible that there is a vacuum leak always present and the car is just more sensitive in the cold since it needs a richer mixture than usual during warmup and the vacuum leak leans it out.

Personally, I'd try everything reasonable to resolve it before getting a tune. When you put in an aftermarket ECU on an engine that already has issues, it makes it very challenging to troubleshoot later if other things come up. You're not sure if the tune is bad, or if the tune is good but there is something else causing the issue, or the tune is bad in a way that masks the issue but then the issue worsens (as they always tend to do) and now you don't know what to do, etc.

 

Understood. That’s also what I was worried about with swapping in the new ECU. I plan on going out there sometime this week to pull apart the throttle body and check the valves and thermowax. I’ll definitely have to check around for leaks as well.

Thank you for the recommendation. If that’s what you’d personally do, that’s what I’ll do as well. I’ll report back if I run into anything else or, in Jeff’s case, if i resolve it!

 

Here is the thremowax in its housing:

polished thermowax

Yeah, I'm showing off!

 

Welp.

I managed to pull the throttle body and clean the valves and make sure the thermowax was functioning. Looked good, but, in hindsight i shouldn’t have done this, but decided to check the BACV before checking if it was resolved.

Everything came off fine, coolant lines are clean, but the very end the vacuum hose on the bottom snapped from the intake pipe. Not the hose itself but the plastic? piece that connects. Broken piece can be seen in first pic. Second pic for reference, the hose came from the part up top.

I’ve been unable to find a part # for replacement or a viable solution, so for right now obviously the car will not start with what is effectively now a giant vacuum leak.

Looking for any possible solutions or replacement parts, because I’m sure the JB Weld i threw on to atleast get the car started won’t be a long term solution lol.

 

It looks like that part is discontinued:

https://www.amayama.com/en/genuine-c...n_cooling/1312

I think JB weld will probably hold for the time being, but otherwise I think you might have to fabricate something custom. If you have any local shops they might be able to make one out of aluminum.

I have a steel one on the Turbo II engine I've been meaning to swap for the last few years, but it's designed for a Blitz blow-off valve and won't work with the stock recirc valve. If you're in the market for a blow-off valve you might be able to find something similar on the used market.

 

Something like this, except hopefully not as ludicrously priced:

https://www.ebay.ca/itm/176636962282...mis&media=COPY

The valve is different but that's the same tube I have (albeit in much better condition than mine).

 

Thank you for this link!

It looks like this would be 13-240D right? The amayama website has this part available, if it’s correct. I might be wrong but it looks like that’s where the pipe would exit for BACV right?

 

I think it would be. I was incorrect about it being discontinued - I think I hovered over the part next to it by accident

 

Does a turbo have a diaphragm that closes the #2 secondary throttle plates when cold? Below 140 degrees F.
I have a NA 88 GXL and as I rebuild the throttle body, I learned that if the diaphragm is ruptured it causes a vacuum leak into the secondary intake manifold.
All the stock diaphragms I have come across are leaking, some a bit, others a lot. To be expected after a third of a century.

In searching for a new diaphragm, I came across one with a part number that starts with 300, I came to the conclusion that this part was for a Turbo model.
If you do have a diaphragm, trace the vacuum line to the intake manifold and cap it off there, see if it changes the idle when cold.

This would be a no-cost test. What does the forum think about this?