ecurbd02

iTrader: (7)

I think that’s a really good idea. I didn’t have much time today but I warmed it up it and controlled the throttle at the throttle body by hand, it did NOT get stuck when I did it that way. So I’m thinking it has to be within the cable/ pedal. I’ll dive into it more tomorrow, but still weird it doesn’t do it when it’s not running.

I’ve attached a few pics of the and highlighted the throttle cable route. What do you think? The tightest bend is the picture from the side.

DaveW

In the last photo, the sharp angle change coming off the end of the metal tube is not good and I wouldn't be surprised if that is the bind point. I make it a rule that I never have a situation like that because even if it doesn't bind, it will wear the sheath lining and fatigue the inside cable.

ecurbd02

iTrader: (7)

noted….kind of my thoughts as well on it but I wasn’t sure how much of a binding point it would be. I’ll have to mess with it to see if I can get a little better of a route.

billyboy

Prior to discs, on bicycles with v-brakes, the manufacturers used a steel tube for tight 90 degree turns at the end of the bowden. Dunno if anyone does a 180, something like that would be the only way to improve matters with that cable run.

Never paid any great attention, I've seen those rotary works TBs on yahoo recently, do they do a version specifically for RHD perhaps? Short of that, remaking the throttle wheel or adapting another one with some sort of cable stop above the plenum for a straight pull, would be the best way.

ecurbd02

iTrader: (7)

So I had the guy come from the shop that helped me finish up the car, he thinks it’s the vacuum on the engine during decel causing the butterfly to stick shut. He suggested drilling a small hole in the butterfly to help alleviate this. Any thoughts on that?

scotty305

iTrader: (2)

Drilling a hole will add airflow, which might raise the idle speed. It can also change how the car feels during deceleration, I think you might have less engine braking with your foot off the throttle.

TeamRX8

iTrader: (2)

no maybe, it will definitely raise the idle speed

which you could possibly do otherwise to see if it can be adjusted out of the “sticking” zone. I didn’t read the thread though to see if that had already been tried.
.

Pete_89T2

iTrader: (4)

^He may be on to something... Different situation & TB, but way back in the early '90s I had similar issue with my '84 GSL-SE with the OEM TB. What was going on was after a quick decel (high vacuum) coast down to idle, sometimes the secondary plates would stay cracked open slightly & flutter, resulting in a high idle speed that would fluctuate. Stomping the throttle in neutral (to cause another rapid change in vacuum) would usually return the engine to a normal idle.

Turned out my TB just needed a very thorough cleaning - a combination of some carbon build up on the secondary plate shaft (I had over 100K miles on it by then) and the stronger vacuum during decel prevented the springs for the secondary plates from fully closing them upon return to idle

DaveW

Similar thoughts in these 2 posts...

ecurbd02

iTrader: (7)

throttle body is brand new, I couldn’t see anything on it the could be cleaned. I maybe have 20miles on the tb? Basically shop-home-around the block a few times. So would the vacuum keep it shut or cause it to open? Mine is sticking shut.

DaveW

I'm confused by what you said here. It can't be sticking closed at 2K RPM. Do you mean it doesn't want to open further once you get to 2K RPM, or what? When it's at 2k if you let off, does it close? Or just not want to open further?

scotty305

iTrader: (2)

If engine vacuum is actually pulling the throttle blade closed, the vacuum will usually be stronger when decelerating at 5000 RPM or 4000 RPM than when the engine is decelerating at 3000 RPM or 2000 RPM. Higher engine speed will pull stronger vacuum on a closed throttle, since it's trying to pump more air per minute.

ecurbd02

iTrader: (7)

i beleive it is stuck closed. opening it further is no issue. Example would be normal driving, shift around 2500-3000 rpm so you let off the gas, shift, then when I go to push the gas pedal after the shift, the pedal is stuck. It either requires excessive force to move past top position (zero throttle) or I have to wait until it gets down to about 1200-1300 for normal operation. There is no rpm hang at any level. I haven’t had it any higher rpm than 4500 due to my break in period, as far as I know it’s stuck as described through the rpm range >2500 which is why it leads me to believe it’s a vacuum/ iac issue. Which I could be completely wrong, it’s just my train of thought.

DaveW

Yup - sure looks like vacuum is causing the issue. My guess is the butterflies must be hanging up on something when there is significant vacuum.

billyboy

Back in the old days, some did drill the throttle blade (and add progression holes) when idle and emulsion circuits couldn't accommodate - that would be a hail mary on mixtures not vacuum.

Does your ecu log MAP? Looking at that cable run again, I'd wager you're under half a minimum bend radius on a bowden cable. I'd still fix that before acting.

I suppose you can silver solder the hole closed, so the mod is not irreversible. If you do proceed, I wouldn't start at your hardware store, 1/16th bit size either! Jet or wire gauge drills are probably what you're looking at. For best results, I'd be avoiding a wonky hand drill in situ - I'd probably resort to turning the pin vice by hand before that, although by rights, for the small sizes, you should be doing 10s of thousands of rpm to avoid breaking them endlessly.

j9fd3s

iTrader: (3)

on my P port i drilled the plates on my Weber, for just the reason Billyboy describes, the throttle plate needs to be in a certain place physically for the idle and transfer ports to work, but the engine wanted more air.
i started with the tiny drill bit set for like a dremel, similar to what your dentist uses. its been a long time, the old days, but i think i ended up at like 0.015" or something. you can solder it closed, or you can on a Weber, the plate is brass. i went up to like 0.030 or something and had to come back down, because the carb still needs some vacuum to actually carburate

or maybe you could just put a bigger spring in the TB, or use the Mazda throttle body which won't have this problem

DaveW

Also, IIRC, usually butterflies are not always perfectly symmetrical in relation to their pivot axis. One side usually has a tiny bit more area than the other. If the side opening toward the TB inlet has more area, vacuum will help it close. If the side opening away from the TB inlet has more area, vacuum may prevent it from closing. Also, flow characteristics are different on the 2 sides because of the plate angle in relation to the TB, so even if the areas are exactly equal, high vacuum could be keeping the throttle open or closed and there may be no mechanical issue causing it. Once the vacuum decreases, throttle-plate motion then would be possible.

So:
If sticking open is the case, then j9fd3s' stronger spring suggestion may be the solution.

If it's sticking closed like I think ecurbd02 meant, then either some bleed holes or a longer radius (larger diameter pulley) to the throttle cable at closed throttle may enable opening. You may need a variable radius pulley like I see on some exercise machines to give more mechanical advantage coming off closed throttle. If the cable force is too high, then your circuitous large-angle-change cable routing could make the cable act like a capstan and cause it to bind.

Capstan ( https://en.wikipedia.org/wiki/Capstan_equation ):
The force gain increases exponentially with the coefficient of friction and the total angle of contact (around the cylinder or in this case, along the cable).

DaveW

So if there is even a small amount of force added to the cable tension, like what may be present in the butterfly pivot due to the vacuum pulling on it, or the sharp bend near the pulley, that multiplies exponentially through every curve of the cable and is, IMO, likely to be the issue making it stick closed.

ecurbd02

iTrader: (7)

totally understand the cable issue you guys are bringing up. My only thing that makes me think it’s not, is when it’s not sticking there’s no variance in amount of force required through the stroke of the pedal and that it’s rpm dependent. Please correct me if I’m wrong, it’s just the way my brain is working when I think of it lol once it gets above 20 deg where I’m at, I’m gonna drill a small hole in the butterfly. I was gonna check the duty of the iac at idle to make sure I have a little room to bring the idle down though

DaveW

Well, what I mentioned and explained is only a possible cause, not 100% certain it's actually that. Good luck with it.

DaveW

"When it's not sticking" - does that mean w/o vacuum on the intake, i.e., car not running?

The capstan reference only applies when there is some extra force to be overcome near and/or at the throttle plates, and that is only present when there is vacuum, i.e., car running. And that, IIRC, is when you said the issue occurs.

j9fd3s

iTrader: (3)

this is a good idea, the IAC adds air, and can change the cell of the map the engine is in, which can change fuel, which if its not right can do odd things to the RPM, its part of the bouncy PFC idle issues

BTW our solutions have basically been if the throttle is physically sticking, like the blade gets stuck somewhere, but it could easily be a map issue

ecurbd02

iTrader: (7)

yes when the car is not running. Ok I didnt realize the capstan reference was in reference to when there is an additional force to overcome. That does make sense though. If it is the throttle cable binding, do you have an idea where I could get a longer cable aside from custom? The USDM cable is longer than the JDM which is why I went with it. The jdm cable won’t reach.

j9fd3s

iTrader: (3)

all of the Mazda ones are basically the same, you might measure up the US Miata cable NA01-41-660A. the pedal is on the left, and the throttle body is on the right front, so its quite long.
you might also try to route yours more like that one

DaveW

I only know custom cable suppliers - the best is "Control Cables." Website: controlcables.com (562) 949-0455
They are well known for supplying push-pull cables for aircraft. I use their cables for the throttle and for swaybar controls on my racecar.
They are VERY good and easy to work with AND THEY ANSWER THEIR PHONE. They can make almost anything you want, quickly and at a reasonable cost.