Cruise control for constant throttle rather than speed?
 

It seems like there would be a way to do this, but I'm not sure how...

The only bump I've been able to get in the mileage on my '96 Suburu Legacy Wagon (auto tranny:mad: )has come from wedging my foot against the tranny hump and trying to keep a constant throttle and let the speed fluctuate between 40mph uphill and 65mph going downhill.

It seems the cruise control could be rigged to do this too, any ideas?

********Update and pics are at the bottom************

just a thought (might be stupid) if you are worried about throttle opening, why don't you do something to limit your play. you could put a restrictor plate behind the throttle body. or an even wilder idea is to put something behind the gas pedal to limit movement. I wouldn't recomend that because there may come a time when you need it.

you could rig up a stop that is on a pretty heavy spring to that you can go past that point if you want to but you will know when you hit it. I am speaking all mechanical that doesn't even touch the pedal until you depress it far enough to contact it. that way you know where that limit is but you can punch it if you need to.

*edit* not as good as the cruise idea but probably simpler to execute

The best way to do this would probably be low-tech, maybe a remote-operated clamp on the throttle cable or something...

A locking throttle cable? Motorcyclists have added these devices for decades. There is enough friction to prevent the return spring from closing the throttle plate, but not so much that a roll of the wrist can't overcome the friction of the grip when a flip of the release lever isn't quick enough.
But in a car there's no easy means of closing the throttle by pulling the pedal up

this may be way out there but you could set up a series of proximity sensors (maybe magnetic since the gas pedal is metal). you could rig up a series of LEDs that could tell you where your sweet spot is. you could monitor this so that it was in the same place (relatively) all the time. this way noting contacts the pedal or restricts your movement and you know where the pedal is and where it should be. it would take some time to rig up and set to the right throttle position though

sorry for overthinking this but it is an idea and I was talking about a completely stand alone system that is not hooked to the car in any way other than the battery.

I believe the Scangauge will display TPS voltage, you could use that as feedback to maintain a constant throttle setting manually.

Hmmm thinking of magnets... thinking a strong electromagnet close to the cable might lock it, then you could rig an on/off switch, with a light sensor override with the beam cutting across the tops of the pedals, so it would cut off immediately when your foot went for emergency acceleration or braking and broke the beam. Well, maybe you'd want to rig a set/reset pushbutton and latch it through electronics rather than a switch.

The easy way to do it is to disable the cruise control from opening and closing the vacuum servo that moves the throttle cable either by fixing the power that keeps them closed or open and yet still have the vacuum release on the brake / clutch pedal for safety. I think I will try this on mine once I get into the circuit a little since it will be easier to increase and decrease throttle if I have control of the valves that regulate the servo. I would also like to see when it is adding and removing vacuum to vary the throttle with a red/green led.

a friend of mine at work told me about the "old" cruise controls they had when he was younger (he is 61). He said they used a throttle cable hooked to the carburator that held the flap open a certain ammount and it had a thumb nut that held it into place. the problem (he said) was that it had no override so if you had to quickly slam on the breaks then you were fighting the engine with the breaks until you released the cable.

I think you could apply this to a throttle body but I would do it with caution. this sounds a little on the dangerous side and thus the reason they don't do it anymore.

hopefully the description above paints a descent picture. I haven't seen it, I am just going off of his description. he said himself that it wasn't verry safe.

The adjustable stop with a heavier spring sounds like the most straightforward idea to me.. Easy and cheap to implement and nothing really dangerous to go wrong like could possibly happen with clamping the throttle cable.