I thought the TB mod would cause problems on cold start as well given my current location. However i found absolutly no problems after doing the mod. You just have to be sure to let the car warm up before ripping on it. The longer I own my T2 the more I realize in order to make my car run properly and reliably I have to rip out just about everything Mazda put in.

 

I think I’ve got it figured out. If you look at pages F2-6 and F2-36 of the S5 FSM it shows everything pretty clearly. (The S4 system is identical, but the schematic in the S4 FSM is crap.) The check valve sits between the thermovalve and the vac side of the TB, and it’s oriented so air can only flow from the valve to the TB. When the engine coolant is cold, air can flow though the thermovalve from port A (the #2 secondary throttle actuator) to the manifold. So when you start the engine, manifold vacuum sucks air out of the actuator, which pulls the #2 secondaries closed. But because of the check valve the air can’t return so the throttles are held closed. Once the coolant reaches 60°C (140°F) the thermovalve changes over so air passes from port A the actuator) to port C, which vents to atmosphere relieving the vacuum in the actuator and popping open the #2 secondaries, which can then operate normally. Pretty clever really.

 

Before or after the TB mod. If it was before, your thermowax was broken. If it's after, what did you expect... Personally I prefer to fix things that don't work on my car, particularly if they perform a very handy function. I stop at several intersections on the way to work before my engine reaches operating temp, and having no fast idle would be a major pain in the ***. That's why mine stays. I'm curious about your proof of that theory. I'm confident enough in my knowledge of fluid dymanics to continue to diasgree with you. Like I said above, I'm going to pull that shaft anyway, so it's a moot point. It sounds like you ran your TB like I plan to so I'm glad to hear it works OK. Thanks for the info.

 

I just got my BDC TB yesterday in the mail I think I'm gona miss the thermowax, which is why the stock TB will stay on till end of winter

http://www.1300cc.com/TB/

I was also planing on just blocking off the coolant line at each end. why do people still run it from front to back???

 

NZ....OUCH! I understand now. Here was my problem. I put the check valve b/t the double throttle diaphram and the water thermo. That is how its done on a n/a. Except on a n/a its a DElay VAlve. Why did I put it there? Because the turboii I have was a salvage vehicle that I bought. It was salvage because it had had a pd fire,plus the joke who owed it briefly before me was a two legged disaster, as a mechanic and muddled up a number of things.

So when I rebuilt the engine and replaced the burnt hose and injectors etc, I put the check valve where it was on a n/a engine (no picture available in the 87fsm) and I didn't realize for sometime that it was not a delay valve, but a check valve. It got removed early on because I said to myself "this is nuts and does not make sense". So it got tossed in the back of the shed. But Its always bugged me how that check valve could possibly work. Now I know. It does not go b/t the water thermo and the double throttle diaphram....it goes b/t the source of vac and the water thermo. Thank you. P.S. Sorry, Christi, to have done this question on your thread. Just saw an oportunity to get an answer to my question.

 

NZ, My secondary throttle plates worked just fine prior to my removing them. It runs great in the summer. Fire it up and she'll stay runing all day long. It's only in the 40's that it doesn't like idling cold. (thats what 4x4 trucks are for here in MN)

Now that I've run the TB mod, I'll be designing a single plenum upper intake manifold and converting to a single butterfly TB. I suppose I should really decide if I'm gonna do the turbo conversion (nowhere near stock) before making my new plenum though huh? Makes a big difference where the plumbing goes.

 

That's interesting. Like I've said before, my car, completely TB-modded, will start and idle stone cold at 600ish RPM. It has no tendency to stall. I don't drive my car cold, but I have, and can say that except for needing a slight bit more throttle when doing a standing start, the car runs fine.

Remember this is STONE COLD (< 50 degF coolant temps).

The best reason for removing the cold start assist is because as the system fails, it will hold the idle high, even when hot. And I can't begin tell you how much high idling bugs me. It's my opinion that the people who have modded TBs and cold-start problems have other issues, like vacuum leaks - with even a single nipple disconnected and vac leaking, my car stops running when cold. When done right, it's perfect.

Just my $0.02

Brandon

 

Something you guys are overlooking here (took me a second to actually realize it) is that I have a HUGE street ported motor and my idle is set very low in relation to where everyone else has theirs when runing this much port. If I were to raise the idle to 1000rpm I wouldn't have the cold air - cold start problems I do. High idles also annoy the hell out of me so I keep it just high enough so it doesn't lope. This translates to a car that doesn't run below 1k stone cold when the air temp is below 45 or so.

I went through everything on my motor when I did the rebuild making sure it all worked to specs. (eliminated a lot of worthless crap too) I have no complaints about how my car runs. It doens't pose any problems during the season I drive it anyways.

Winter cars here in MN end up on nature's diet (lots of rust) and I won't let that happen to my 7.

 

just to throw in my tb mod expierience regarding cold starts-we just had a cold spell a few weeks back where temps where in the upper teens-my car started and idled just fine[exept for a loping idle for about a minute,wich i belive is a tps problem].i have never had any problems,but i also let it sit till the temps start comming up on the temp gauge[120*]before driving.
d

 

You live in Florida. It gets a little colder here in Auckland. And remember the thermowax system has no effect on how the engine runs, only how it idles. All it does is open the primary throttle plate a bit. Again, not cold-start; cold-idle. And if it wasn't needed as you say, Mazda (and every other manufacturer) wouldn't have fitted it. It comes back to climate. The 7 was sold in places a lot colder than Florida, including Japan! If it works okay for you that's great, but that doesn't mean it'll be okay for someone else, even if there car's perfect.

 

Any chance you could post your dyno sheet, or give us a few RPM points comparing the difference?

Thanks.