OptionXIII

This thread is to document what I've done to get reliable service out of my Skunk2 Throttle Body. I've had it installed for a year, during which time I've racked up 10k miles, including two track days. The engine is otherwise completely stock, down to the intake crossover pipe and ECU. This was only done for durability. I'm not on track as much as the guys that typically have the issue with eating a screw, but I didn't want to take chances. Of course, being a crappy part, it has a ton of issues of its own that should be addressed and will probably make my car worse overall.

These are the issues I've encountered myself or am otherwise aware of through my internet research.
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1. It has a larger ID. Port match the intake manifold for best flow.
2. Idle control issues.
3. Included hardware is generally wrong and can vibrate loose.
4. Throttle cable barrel breaking off.
5. Intake crossover tube needs some persuasion to fit over the larger TB inlet. Warm it up, use some lube, jam it in there.
6. S2 TB has no provisions for the throttle body coolant path. I used a brass hose barb to connect the two coolant hoses so the stock coolant/oil heat exchanger still gets coolant flow.

1. Port Matching


Install the new TB and use a sharpie to mark the material that needed to be removed from the IM to match the new TB. I jammed a rag into the intake, then taped over top of it to be absolutely sure no shavings would get in.


The patient after surgery. The die grinder made quick work of this.

2. Idle Control Issues

It's a pretty common experience to have idle control issues. I see two problems with the new TB - there is insufficient tension on the spring to keep the throttle plate closed at idle, and the IACV ports are miniscule when compared to stock.


The S2 throttle body doesn't seem to have enough tension at idle. I drilled in some adjustment holes (stock is furthest left). Currently set to the least stiff new option, the second from left (red arrow)

Some people have had issues with the spring itself breaking. I recommend you drill multiple additional as I did, and experiment to find the least additional stiffness you can use without having an intermittent high idle.



The original TB has truly massive ports that lead to and from the IACV.



In comparison, the Skunk2 TB ports are tiny and convoluted. I you can see I cut away some material hoping to improve the flow. I recommend you be more aggressive in doing this. I plan to remove more material in the future.

3. Fixing the Hardware.

The IAC mount has a blind bolt that I needed to shorten to clear the IAC itself that is mounted over it. You can see it in the picture above. One external IAC bolt just needed a washer. One external IAC bolt wasn't included. I am Loctiting anything that doesn't need adjustment.

Four socket cap bolts are included for mounting the TB. They expect you to remove the top two studs that are installed in the manifold and replace them with the included bolts. I like how the studs hold the TB in place before you bolt it down, but the S2 TB is shorter than factory and the nuts will not thread down far enough to hold it in place.


I cut out some top hat looking spacers to tightly fit the TB and factory flange nuts.


Mounted and ready to adjust. I used the supplied stainless socket cap bolts on the bottom of the TB.

4. Throttle cable barrel breaking off.

Some people have had an issue with the throttle cable barrel snapping off. The Skunk2 TB has it's own hard stop at the throttle body itself. Even if you adjust the stock throttle pedal stop to prevent the TB from hitting it's own built in stop, is not stiff enough to prevent tension increasing on the throttle cable if you've got a heavy foot. My belief is that the people snapping these off have a combination of higher redline, more power, and haven't accounted for pedal box flex in their throttle stop adjustments.

I've heard of it breaking off on high power track cars in as little as two laps of use.

The original plan was to use a set of feeler gauges to get the throttle just shy of hitting it's own stop when the gas pedal is pushed to the floor. That didn't work out because of the pedal box flex, resulting in more throttle cable travel even after you hit the pedal stop.


With some homemade bracketry and TIG welding, the pedal box flex is sorted and now have the worlds stiffest Miata gas pedal mount.





With that taken care of, the max pedal travel was set so that the Skunk2 never hit its own throttle stop.

My recommendation for most people is that you add a hard stop to the pedal on the floorpan. This would be significantly less work.


One year later...

So after a year of use in daily driving, road trips, and two track days, I have had only one issue with the Skunk2 Throttle Body. When it gets to 40f and below, the engine occasionally stalls when returning to idle from clutching in or going to neutral while coming to a stop during warm up. Usually this only happens at the first two stop signs in my neighborhood. By the third stop sign, it's only a little erratic. I haven't driven the car much below freezing and can't comment on colder temps. My belief is that the terrible IACV ports add some additional flow restriction that the factory ECU is not able to account for. This slows the responsiveness of airflow through the IACV and results in a stall.

Otherwise, it behaves exactly like stock. I'll update if I ever run into any issues.



A lot of what I have written is already public knowledge and covered in the thread linked below. Shout out to Curly in particular for sharing his experience.
Skunk2 Throttle Body Sticking?! - Miata Turbo Forum - Boost cars, acquire cats.

Most of this is carried over from my build thread. Shameless plug for that, but I wanted to make something that was more easily referenced.

OptionXIII

My intake manifold had to come apart a few weeks ago, and while it was in pieces I decided to revisit the IACV ports due to continued stalling on warm up. Based on other peoples success with epoxied stock TBs, this was a make or break moment for the S2 - either it stops stalling, or I go back to stock.



This time I was much more aggressive in how much material I removed.



Here you can see how I cut material away to the edge of the gasket. To seal up where I slipped with the file and scratched up the sealing surface, I used anaerobic gasket maker on the TB side of the gasket.

This morning it was 29* out. Even though my car is parked in a heated garage, these are the exact sort of conditions it would stall out in previously. I had a pretty bad idle oscillation at one stop sign, but the engine didn't stall, so the S2 gets to stay.

While I am going to keep running the S2, if I could go back in time I'd probably stick with a stock TB and epoxy due to the amount of work required for this to play nice with a stock ECU, and the failures other people have had with the S2. The stock TB will get epoxied and come with me to track days as a spare in case a return spring or throttle barrel failure happens to me.

Fireindc

iTrader: (13)

Sweet thread man. I've had one for 3 years now, dozens of track days, no issues and mines been running fine. Loctite all the things, had a buddies at the track basically fall off. I'd mention the IAC issues you are having are non-issues on my ms3 with good tuning. Plenty of idle valve adjustment on the standalone to keep it from stalling or doing strange stuff.

I noticed a much lighter throttle pull than stock, even after the spring mod. That coupled with the larger diameter butterfly means a much snappier throttle, both good and bad depending on how you look at that.

I'm actually surprised you've had such success with the stock ECU controlling this, props!

Gee Emm

It uses the stock idle control, so the stock ecu should control it ... ?

I never had any issues with any of mine, after the initial prep. I was interested to see your mod to the port, I don't recall ever doing anything to that. However I have just replaced the idle control itself due to a hunting idle, job done, hunting gone. I'd suggest you try that if still won't idle correctly.

Fireindc

iTrader: (13)

Is yours on stock ECU as well?

Just because it uses the stock valve doesn't mean the PWM values are exactly the same. I.E. different amounts of air getting in through the closed throttle body, vs stock (there's always some amount getting past), and of course the way the idle valve mounts is different with a less direct path, like OP was describing.

I figure it would work, but wouldn't be surprised if it wasn't perfect.

Gee Emm

Not this one, the first of them was though - had no issues.

I guess my point was the IAC is not failure-proof, I just fixed a problem sounding a lot like the OPs by replacing the unit, no cutting or grinding required (though that might help its performance).

OptionXIII

Crap. I failed to pull off a spare TB out of the junkyard on the "$75 for all you can carry" day. It would have been free. Given how quickly Miatas get attacked in the junkyard, I don't know if it will still be there should I go back tomorrow.

Maybe I'll try giving it a clean.

Gee Emm

Good luck, cleaning is worth a try, but it didn't help mine - hopefully you will have better luck though!

LeoNA

These are not a bolt on without tuning regardless if it is on an oe ecu or stand alone. The real issue is the bypass adjustment screw which has a poor geometry. The taper is steep so a fraction of a turn has a large affect. On a stand alone the tuning is straight forward because you have a metric. With the oe you have tune to compliment the range of the IAC. If it stalls then the IAC is out of its range. It’s either fully closed and there is still too much air or the opposite. From the manufacturer the screw is either hard bottomed or loctited. They are soft brass and slotted. The slot strips easily so use a good fitting driver.

SlowTeg

I just wanted to log my results. After one track weekend the junk2 started hanging bad for me with the hole drilled in the same spot as OptionXII. One problem after the weekend I noticed is that the (13mm) nut backed off a bit. After snugging it back down I noticed there's a bit of friction at some points when rotating the throttle rotor. This is undoubtedly causing the hang. Not sure if the nut loosening a bit caused the rotor to allow some side to side wobble and shifted the spring or what. After removing the nut, I could see the spring is binding a bit on the plastic bushing (there are score marks in it). It's also worth noting the bushing is larger than the shaft so there is some play in it.




After removing the nut/rotor/bushings/spring, I wanted to check if there was friction in the main bearings and throttle shaft. The good thing is there isn't any, so all the friction is in the bushings/spring/rotor somehow. I reassembled it with the same hole as before and it felt smooth now.. interesting. I hit the spring with some silicone spray (hopefully prevents binding) and drove the car and am happy to report it had zero hang whatsoever. Granted it was only one day but interesting to note the issue is definitely in the spring/bushing/rotor. I will report back as time goes on. It might be a good idea to lubricate the spring right from the start.

SlowTeg

On some further thought I gotta wonder if the bushing having a much larger inner diameter is the main problem. I didn't grease the inside of the bushing/shaft but in hindsight I'm thinking I probably should have. The bigger question is why the bushing is so much larger than the shaft. As it heats up and spins a bit over time it starts binding and adding friction. My initial thought would be a more snug bearing and some grease might be the real fix?

LeoNA

I doubt that is the issue, most if not all torsion springs use a spacer to reduce the distortion of the spring at max travel. The later S2 TB's supposedly have a stronger spring. I have no issues with mine. I have seen many throttle cables adjusted incorrectly where the TB is used as the stop. This will eventually bend or break the throttle shaft. The proper way to set them up is to have someone hold the gas pedal firmly to the floor firmly and check the throttle position. It should still be able move a small amount towards the open posistion, hence not be on the throttle shaft stop.