While driving a bus, I was pondering the throttle body mod. I'd like to simplify the throttle body and get rid of the thermowax, but I also live in a cold climate and don't want to have to hold the throttle to keep it running until it warms up.

Busses have a "high idle" switch that kicks the idle RPM up - useful in the cold to keep the engine from cooling down too much (there's no thermostat. In 0F degree weather, an idling diesel does NOT stay warm).

If the BAC and PS/AC bypass valves were kicked to 100% percent open, they should provide enough air to bring the idle up to 1200-1500 RPM. I haven't tested this yet (mostly due to not having enough time to even look at my car lately), but this could allow for an electric high idle.

Has anyone tried this? If it's tied to the water temperature sensor, it could be automatic - high idle until the engine is warmed up. If there's a switch attached, this could also be used for cold weather running - my alternator doesn't "kick in" until 1000 RPM or so, and if I have a high electrical load, I prefer to idle above 750 RPM. This could be implemented on an ECU piggyback board (tied into the harnesses) easily enough.

-=Russ=-

 

Thats actually a pretty inovative idea. I don't see why you couldn't do something such as that.

 

just a thought that popped into my head that should work (i am pretty good at thinking up ways to rig things but in a good way...). find a spare speed control servo and set up a stop on it, hook the servo up to manifold vacuum and a power supply switch to open the valve and you could adjust the high idle speed at the cable or servo adjustment.



the best way to provide a stop would be to allow the servo to bottom out and either cut down the stock cable or find another slightly longer cable so that the throttle could not be fully opened by the servo because it cannot be limited as it is a diaphragm, i would have to check the design of the actual motor on these units, there is several different types of SC servos and one might suit this proposition better than another depending on how you chose to set it up.

 

This sounds liek a pretty cool idea too me. I am not in a COLD climate, but it gets cold enough to make early morning a PITA without the thermowax.

I am just waiting for NZConvertable to jump in and say I told ya so...

 

I use my BAC as a high idle on my car.. however.. the BAC isn't an on/of type valve... it has to have a pulse rate to it for it to work... I set it in the Haltech with a target idle and a millisecond pulse rate...

 

I know it's not a on/off valve... but a constant 12v to it should lead to a 100% duty cycle.

Since you're here: What's your "high idle" RPM, and what percentage of the time does the BAC spend open to maintain it? If it doesn't require both valves wide open to hold 1300-1400 RPM, that makes my life easier (well, sort of). Just implement a PWM circuit and set the required duty cycle. If the car's warm, the ECU controls the BAC, else the PWM circuit does.

... I've just realized I'm going to end up building my own RX-7 specific standalone ECU by the time I finish all these various projects.

-=Russ=-

 

Well, I'd like to point out that this is already done by the factory. That 3000 RPM startup is created by opening up the ASV and BAC.

Many people with standalones will leave the ASV installed and use it to control the high idle during warmup, AC operation, etc.

In the factory configuration, the BAC is mainly responsible for maintaining the idle once the car has warmed up, while the ASV comes in when the power steering loads the system.

 

Man, if there is a way to safely do this I'd sure be interested, I have my thermowax stuff off at the moment and miss the cold start at times.

 

That's what gave me the idea. A 3000 RPM idle is a bit excessive though.

-=Russ=-

 

I told ya so...

 

take manual control of the cruise control?

 

Well, if you want, you can put a switch on the ASV. But why not just leave the thermowax and have the car do it automatically?

 

Yeah, I'm thinking seriously of putting the thermowax back. Unless someone comes up with a n easier way.

 

Same here. It will take less time to reinstall it that to sit in my driveway and wait for the car to warm up with my foot on the gas.