raising the idle... manually or automatically

Ok. Basically what I want to do is figure out the best way to raise the idle of my engine at any particular time for various reasons. One of the main reason being that I installed a york compressor OBA system and while it is awsome at idle, it flat out cooks at 1500 or so. Ive been toying with some ideas on how to do it. I want to be able to flip a switch and have the motor idle at or around 1500. Or...even if there is a good way to do it with a cable. Im open to suggestions. Ive heard that there is a way to do it through the vehicles electrical/computer systems. Couldnt find much from searching, so anyone with any ideas post em up! Jeep is a 94 4.0, auto. Thanks in advance. One of these days ill post pics of my york installed and how i did it all. Came out real clean and works better than the shop air in my garage.

Justin

Its been said here before that the Police version has a High idle switch.Dont no how they accomplished it though!

well - there is a hand throttle that people use for on board welders and on board air...

try a search for hand throttle

and i know there is a tech write up on xjfanatic.com

Emulating the "Extended Idle" function is on my list of projects in the Someday file - I'd like to have that myself.

Meanwhile, here's what you can do...

Go to any industrial supply shop (that does forklifts and stuff) or check out www.aircraftspruce.com or www.wicksaircraft.com for "control cables" - they usually have some sort of "friction lock" on them so you can set them and lock them so they don't wander - and also the industrial versions usually have a "slap" knob so you can override the friction lock - and any "unscrewing" you have to do to make it move - and turn it off all at once.

Put the knob in a convenient place, and run the cable thru the firewall toward the throttle.

Connect the cable to the throttle arm (usually on the side where the cruise control connects, so you can "pull" to open the throttle) using a couple inches of bead chain or other light chain (so you can operate the throttle normally wihout messing with the cable) and fix it all in place.

This is roughly similar to how an add-on hand throttle would be connected, but it will give you the ability to "lock" the throttle at high idle and unlock it easily. I'm sorry I don't have pics - I haven't had a reason to do it just yet (haven't added enough electrics yet - but I've got the alternator!) and therefore haven't planned the mod.

5-90

You can bump the idle some by putting a switch across the pressure switch on the power steering. The switch is activated when you turn the wheel to the lock position, putting a higher than normal load on the engine. When the switch is triggered, it bumps the idle. The same thing happens when the AC compressor is on, but the PS switch is real easy to piggyback another switch across.

Hey thanks for the sites! I have seen plenty of hand operated cables around, but they are all cheap and dont seem like they would work good. But those sites have some nice ones.
The PS switch huh? Ill have to check that one out. Im actually trying to have it all be automatic. I mean, the compressor comes on and off by itself, so I figured it would be cool to have the idle go up automatically when the compressor is on. But... I would also like to manually override it, and bump the throttle myself. I might be making things too complicated, over engineering perhaps. I just like to get myself into messes

Old man: Do you know how much piggy backing the PS switch actually bumps the idle?

Thanks for the ideas!

Justin

Those sites have stuff for aircraft kitbuilders and experimenters - and their catalogues are free. Might want to get at least Aircraft Spruce, it can come in handy.

I'm sure there's a way to do it. I didn't think of the PS switch - I'm not sure I have one. In fact, I'm pretty sure of it - when I did the entire PS setup on my 89 Limited a couple years ago, I didn't see anything electric on the system.

I might have to pillage around (I've got FSM's for 1991 and 1992 - might be able to find something useful there) and let you know if I turn anything up. I'm pretty sure there is a way to do it automatically - how do you trigger the compressor clutch? Pressure switch in tank?

5-90

It bumps it a couple hundred rpms, just enough to keep it from stalling.

That PS idle adust switch exists only on the 2.5L.

It connects to a line going to the ECU( pin 10).

Maybe it still works on the 4.0 ECU ?

What about using a idle solenoid from domething with a carb? i would imagine that you could get this to bump the idle up by about 1000 or more. If you look at them on the car they have a gap of about 1/8 to 1/4" from the spot the contact on the throttle shaft. if you adjusted this to almost touching at idle then it should move the shaft even more. plus the whole leverage thing.

As far as getting it to be automatic, good idea but what about when you are sitting a light and it kicks on? In theory you could connect a wire to the neutral safety swith that would only let the idle come up automoatically in park or neutral.

Dingo

The EXT idle in police jeeps only goes to 1000rpm. Not really worth it IMO.

i remember reading about the idle bump on the police editions, and it sounded very very easy to wire, but not possible on my '88. I forget what year it started, probably 91 with the many other changes.

5-90: Yeah I have the compressor hooked up to a pressure switch which is installed onto the temporary tank. Not sure if its my final setup, but it works perfect. During use the compressor kicks on at 80psi, and turns off at 120psi. Seemed like a decent setting for the limits of the tank and my working pressure. The entire system is energized by a toggle mounted in my shifter plate. (its really easy to run wires and install switches with nothing but seats and a console for an interior )

Dingo509: Actually that was the idea that I started looking into today. The idea of using an idle control valve or solenoid of some sort. I work at a parts store so I was messing with a bunch today at work. Most of the ones I had on hand had like 4 wires to make them operate. Couldnt make any of them work with just test leads hooked to a battery so I gave up for the time being. I didnt find any that actually pushed on the linkage of a carb.... those would be ideal. All the ones I looked at were the "pintle" type. If I did get them to move, it was only a slight movement. As far as it coming on while at a stop light... I pretty much keep the power switch for the compressor in the off position unless Im using the air. In the event that I forgot to shut it off, I suppose I could hook something into the neutral safety switch like you said. I would really like to make the idle control motor idea work. Simple, can be made automatic, adjustable to whatever RPM i want. Just got to find the ideal part.

My curiosity about that PS switch dragged me out of bed and I just double checked outside. I cant see any switch. Ive replaced almost all of my PS components and after I thought about it for a minute I didnt remember seeing any elec components... So I guess it only applied to certain motors/years as stated.

Keep the ideas coming! I smell a good write up if something works good! Anyone have any ideas on what kind of car/truck woudl have a idle control motor that would work?

Justin

You might try looking at most of the GM carb. equipped motors, like Olds, Buick CADILLAC, anything that had A/C should have had the "stepper motor" that you are looking for. Any way, THANKS, 'cause now you have got me walking out-side to look at the caddy parked in the side yard. (Some-times, I really hate having a tendency to to try and figure things out.) Oh, yeah, the motor that you want is self grounding thru its' mounting, and has ONE wire . HHEYYY- if you can figure out how to mount it, then you can just hook it to the compressor trigger wire, so that it would cause the idle to increase as needed. Now I REALLY have to walk out-side and look. Thanks, dude, for making me think-lol. Ren

OK, here's a thought -

Take the AC Idle Boost circuit, and break it through a relay. Trigger the relay with "one of three" -
The original signal can close the relay
A toggle switch can close the relay
The pressure switch can close the relay.

How about this -
Go to your ECM underhood, locate pin 29 (16 gage, light blue. It will be in the middle row, two pins away from the screw that retains the connector. According to my FSM, it's on the right - but I don't know if it's a connector view or a harness view.)

If you tie that terminals to positive voltage, the ECM is triggered to retract the IAC motor pintle and increase idle speed. I don't know how far it will go - but you can check by pulling the AC Compressor Clutch lead, trip the lead from pin 29, and see what happens on your tach.

It may take a diode to prevent feedback to the AC and tripping the AC compressor when you don't want it - unless you've already pulled the Sanden.

Oh - and my wiring diagram here shows that the PS switch is on the 4 cylinder - which makes some sense. The 4.0 has so much torque at and off-idle that it probably won't notice the pump at full pressure...

Remember - this is data from a 1991 (the only FSM I have in that range - or I go back to a 19 or up to a 97) so you might have to check to make sure...

5-90

ren said:

You might try looking at most of the GM carb. equipped motors, like Olds, Buick CADILLAC, anything that had A/C should have had the "stepper motor" that you are looking for.

Click to expand...

I just worked on a 88 ford p/u with a/c and a 78 ford p/u with dealer installed a/c and both had the high idle solenoid. so there's an application. I am heading to the wrecking yard tomorrow for such a solenoid and a high amp alternator to build an onboard welder, so i'f i find something i'll let ya'll know

5-90 said:

How about this -
Go to your ECM underhood, locate pin 29 (16 gage, light blue. It will be in the middle row, two pins away from the screw that retains the connector.

Click to expand...

I tried this recently on my 91 and got nothing, the pin was there on the computer but the hole was blocked so there was no wire. i tried 5v pos then both 12 pos and neg and got no change at all. YMMV

5-90 said:

Oh - and my wiring diagram here shows that the PS switch is on the 4 cylinder - which makes some sense. The 4.0 has so much torque at and off-idle that it probably won't notice the pump at full pressure...

Click to expand...

IIRC the ZJ's had a pressure switch on them however, but im not sure what the difference would be computer wise.

Dingo

I just used the shifter and cable from a mountain bike it works great and is high quality. Just make sure to get a good after market one or one off a good bike.

Just to add to this....



This diagram is for a 96+ XJ 4.0. The police package extended idle switch merely gounds a pin at the PCM which then raises the idle RPM. From what I have read in the factory manuals, the idle will rise to 1000 RPM only when in park or neutral. I have looked on my 96 at the pcm connector and wire and pin is present, it just goes to the bulkhead connector and stops right there. So to wire up my own extended idle switch I would just need to ground that wire through a switch. I have checked on the earlier models, 91 to 95, and there is an input for the power steering pressure switch. The pin connector and wire is missing, but the pin does exist on the PCM itself. Just need to steal a pin connector and wire from a junk XJ PCM connector.

I do also remember that Toyota's use a idle air bypass solenoid. You could rig one of those up if you need more than 1000 rpm. Not sure how much you would get, but it would be cheap and simple to do.

Bryan C. said:

I do also remember that Toyota's use a idle air bypass solenoid. You could rig one of those up if you need more than 1000 rpm. Not sure how much you would get, but it would be cheap and simple to do.

Click to expand...

Any ideas what toyota i'd be looking for? i am heading to a wrecking yard tomorrow.

Dingo

I had an 85 Ford LTD, 3.8L, that had an idle control solenoid/motor that would move the throttle blade with an extending shaft. I think that's what you're looking for. I think it was about 1.25" diameter, about 3" long. I don't remember how many wires though. Pulling the A/C clutch fuse, and turning on the A/C only raises the idle by about 100 rpm or so. It works great for when you want the aux fan on all the time though. This is it right here:
http://www.partsamerica.com/Product...S&mfrpartnumber=77910500&parttype=487&ptset=A