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03 Forester 2.5X 4 Speed Auto
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Discussion Starter · #1 ·
I need a way of holding 2k rpm while I'm not in the car, with a bit of a load on the engine. Looking for a more elegant solution than tightening the throttle cable whenever I need to do this.

I was thinking, does the engine have some sort of RPM-sensor? I couldn't find anything on google. What if I were to put a potentiometer or something in there to fool the ECU into thinking the RPMs are lower than they really are, forcing it to increase accordingly.



Application is this: Stereo competitions, can't be inside the car while competing, need to hold RPMs as close to 2,000 as possible without going over. There's a rule set we have where the motor cannot exceed this speed. That being said, the alternator I have will do 215 amps at idle, 390 amps at 2000 rpm. Once that kicks on, the RPMs will drop back down to idle because of the load, and I can't be in the car to give it more gas to compensate. So I end up losing a bunch of power and it hurts my score
 

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2007 FXT vf37 swapped 4EAT w/ VDC
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782 Posts
The power fc in my other car has facilities for different idle rpms for a/c, defrost, etc. I'll poke around in the open source settings and see if there's something similar in there. I'm almost positive it is.

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2003 Forester XS 5mt
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61 Posts
external tach on hood or engine bay. 20$ rc car remote set up and some brain power....id hook a servo the cruse control cable or you may even be able to wire the crusre into the the rc car receiver?
 

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2012 Forester 4 speed auto
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1,151 Posts
The Dealer

Take the car to the dealer and have him change the idle speed setting on the car's computer. A very simple procedure and the easiest.
 

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2007 FXT vf37 swapped 4EAT w/ VDC
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782 Posts
RomRaider has 3 tables: Low Load, High Load, and A/C. Seems like high load would be just the ticket.
 

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03 Forester 2.5X 4 Speed Auto
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674 Posts
Discussion Starter · #9 ·
I've tried the throttle cable thing in the past. Set it to 2k, RPMs drop down to idle with a load on it :(


Tricking it is a good idea. I'm not sure how I would go about that though. Google is fairly sparse on info for an idle-speed sensor of some sort. Either that or I'm not using the proper key words
 

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All I would do is find something that is the right size to place by the throttle stop where the cable linkage rests when the throttle is closed. I regularily use a screwdriver at work to bleed cars @ 2000+ rpm. You just need something that is safe and secure.

Anything else that can be triggered from inside is unsafe in my opinion. Tricking the IAC is a lot more difficult than a small vice grip on the throttle stop.

If its throttle by wire you will need to use a second pedal with a cut return spring, there's 2 potentiometers in the pedal and its hard to simulate high idle with resistors without triggering a code that will put the throttle into limp.
 

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1999 Forester S Turbo 5MT
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United States Domestic Market. I'd go with Burwood on this, make up some small adjustable mechanical and removable device to fit on the throttle cable where it exits the sleeve/adjuster mechanism. If you can make something, preferably in metal, aluminium should be fine and easy enough to work with, that will clamp onto the housing but have a screw threaded adjuster device at the mid way point between the throttle wheel and the inner cable exit. A downward facing screw in a tapped plate on the device will work nicely, to push the cable thereby increasing the idle speed, but you might want to make the thread on the adjuster an "interference" fit or incorporate some locking mechanism to stop it coming undone again. Using such a device will allow you to make fine adjustments when the amp hits peak current draw and loads the alternator.

When your segment of the competition is done you can either undo the screw or just remove the whole a device thereby not interfering with daily running and safety. Having the ECU modified could have other ramifications, even temporarily.
 

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03 Forester 2.5X 4 Speed Auto
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674 Posts
Discussion Starter · #13 ·
Been poking around on RC controllers and... Well.. Brake handles. I'm not really skilled at custom fab work, so it may be tough.


How is the motor speed read on this car? What sort of output is it? Change in voltage? Change in resistance? Pulsed signal? Trying to see what would be involved for programming an arduino board and a motor or something to control the throttle for me.


I'll reiterate: Whatever I do needs to hold the same RPM regardless of load on engine
 

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2008 Forester X Premium 5MT
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8,064 Posts
Look into a high idle speed govenor for a older gasoline truck with PTO.

At the simplest it is little more than a second cable that attaches to the pulley at the throttle body that is run by a servo controlled by a brain box that needs a tach input(think of it as another cruise control based off RPM not vehicle speed).

You set the target RPM it raises the idle to it, as load increases and RPMs drop it throttles up more.

Haven't installed one in over a decade and am way out of touch with what is out there now(don't spend any time on the farm any more) but some of the farm/ag service sector should be able to point you in the right area.
 

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1998 Forester S 4EAT
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How is the motor speed read on this car? What sort of output is it? Change in voltage? Change in resistance? Pulsed signal? Trying to see what would be involved for programming an arduino board and a motor or something to control the throttle for me.
The ignition coil is the tach output (negative wire IIRC)

Look into a high idle speed govenor for a older gasoline truck with PTO.

At the simplest it is little more than a second cable that attaches to the pulley at the throttle body that is run by a servo controlled by a brain box that needs a tach input(think of it as another cruise control based off RPM not vehicle speed).

You set the target RPM it raises the idle to it, as load increases and RPMs drop it throttles up more.

Haven't installed one in over a decade and am way out of touch with what is out there now(don't spend any time on the farm any more) but some of the farm/ag service sector should be able to point you in the right area.
Brilliant! a PTO speed govenor might do it.
 
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