So I recently bought a 1981 300tdt and ive only had 1980 and before cars before this. All of them had this little "high idle" knob to help with cold starts and etc. Come to find out my 81 doesn't have this, although its not completely necessary its a good little thing to have.

Also my cruise control "computer" is not working so I decided to turn the crusie control motor into an electric "high idle". I guess this could also work as a Manual cruise control but would be very unsafe. My system has no safety and cant decel (although it could, will explain below)

Basically as simple as one on/off switch for the solenoid (or whatever the thing is called that pushes all the plastic gears together) and one bump switch for the motor which will pull the throttle to where you want it and hold it there. Until you turn off the solenoid switch

Heres a simple bench test




And pic of the inside. (notice how the spring is sitting in top right of the pic. Cuz if you decided to take it apart like me it will probly pop out and its hard to get it back in)




Now to the plug. The only ones I need were pins "4 & 5" and pins "6 & 7"




12v on pin 4 and ground on pin 5 spins the cruise control motor "forward" and pulls the throttle out. I put 12v on pin 6 and ground on pin 7 to activate the "ON" solenoid. You can swap the polarity on 6/7 but you CANNOT on pins 4/5 (explaination in next pic below this one)




If you swap the pin 4/5 polarity and put ground on pin 4 and 12v on pin 5 the cruise control motor will turn "backward" thus pushing the throttle back in. This is where I stopped and thought "hey it would be cool if I could control forward reverse reset and off manually" Cuz in theory you could use this as cruise control and you would have a separate switch for accell and decell but it really would be unsafe unless you rigged up a kill switch to the brake pedal or brake lights.

I was gonna get into just to "say I have it" and show people but all I really wanted was a high idle and this alone was too much wiring to make my head hurt, didnt wanna do anymore.

Anyway heres the pic of how you make the motor turn backwards (decell)




I was originally just going to use one on/off switch, connect the solenoid and the motor together and just turn it on all in one. But this way you have to change the throttle arm to a chain or something to make it not rev up all the way.


Next you just jimmy rig it into the car the best you can. I used 10 gauge butt splices to just plug right into the plug with my ACC wire and my grounds, not sure if thats what they are used for but it worked haha.

Blue is ACC running to switch inside the car and white is ground (first pic shows where I grounded it)





I ran the two blue ACC power wires through one of the empty ports where the wiring harness goes through the firewall.




Into the car zip tied up the steering column with some other wires. Make sure you do them one by one and tag them or use different color wire.




Next I wanted continuous 12V power because I wanted to be able to turn up the throttle a little before I started the car for those days that u gotta give it a lil pedal to keep her going. In hind site 12v power that only works when the key is on would have been fine too because I could just adjust the throttle while im waiting on the glow plugs.

But whatever. I used the cont power to the clock, spliced into that with a in-line fuse and split that for power to each switch.




Next I found a good tucked away ground in the car, I used a little screw above some relay above the ebrake release handle. This ground is only for the little red LED on/off light on the switch. But this was important to me for safety reasons. If that light is on. that little button can control my throttle.




Now everything wired up and cut to final length before wire tucking and fit up




Annndd final install. On/off switch with LED for the actuator and the bump switch for throttle control.




Once the on/off switch is on you can bump up the throttle/idle a little bit at a time and it will hold there. But if you over shoot it you have to turn off the solenoid switch and start over, but you get the hang of it after a few times using it. This is where wiring a third switch to be able to back off the idle would be cool and come in handy. But it just wasn't worth the extra headache to me.




Sorry for the crappy grammer crappy pics and crappy videos lol it take a lot more time and effort to make one of these threads than I imagined lol

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Very interesting!
I hadn't thought about the possibility of using the cruise control to allow for something like this, Neat!

Now I wonder how difficult it will be to do something to allow high idle along with normal cruise control operation.

I spent an enormous amount of time figuring out the cruise system and tracking down the problem on my blue car, and made a gigantic troubleshooting document and 3 part youtube series to assist in solving cruise control problems.
And I'm going to bet there is some simple way I could modify the amp or associated inputs to make it a fully adjustable high idle with a settable RPM target and have the amp adjust the throttle to keep it there.

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1982 300D (w123, "Grey Car")
1982 300D (w123, "Blue Car")
2001 Ford F150 "Clifford" (The Big Red Truck)
1997 Dodge Ram 2500 12V Cummins
1996 Dodge Ram 2500 12V Cummins
Previous Vehicles:
1995 E300D, 1980 300SD, 1992 Buick Century, 2005 Saturn Ion

why not use a normal high idle solenoid?

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1977 240D auto w/OM616.916 engine
2005 Matrix 5spd
2006 Prius

https://photos.app.goo.gl/AdP7i8xfCJeFuk5y9

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because this is funner, damn near free, has the abilty to pretty much do anything to the throttle, and winter time is BORING for a guy who does concrete for a living!!! HAHA

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HAHA i think I watched your videos to get my bearings. Couldnt have done it without you!!

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just remember that servos can fail in any position, leaving your throttle stuck anywhere from none to full.

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1977 240D auto w/OM616.916 engine
2005 Matrix 5spd
2006 Prius

https://photos.app.goo.gl/AdP7i8xfCJeFuk5y9

glass pendant necklace http://glasspendantnecklace.com

fused glass pendant http://fusedglasspendant.com

it being hard wired seems a lot more safe than trusting the "computer" then imo. and the off position is pulled back with a spring so it getting stuck Iimthe on position almost seems impossible to me.

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Because the OM615/616 and early OM617 has the injection pump governor intentionally misadjusted for a very low governor idle rpm. Because of this the pump can't compensate automatically for changes in load at idle (AC, power steering, electrical draws) and the RPM can drop. 82+ the governor is adjusted properly from the factory and compensates automatically, thus no need for a knob (which will not make much RPM difference on them).

Thats what gives the 240D and manual 300D's their "jerky" reputation if you lug the engine to under 2000rpm, you're fighting the governor wanting to bring the engine back to "idle".


Because if on the OM617a the throttle is held constant and the engine revvs above 1000rpm without a load it will accelerate to redline on its own. The 615/616 is somewhere around 1500rpm.


Which also means this "high idle" is not safe for the engine...

Brake kill switch could use a relay using the NC contacts and switch open when brake power is applied. Or... you could use the cruise stalk to control all of it and use a latching relay thats cancelled by the brake light.

haha ya I did notice that it isn't as simple as just bumping the throttle up and leaving it there. If I go to far the engine wants to run away. And once is gets warmer it seems the rpm will go up when throttle position stays the same. This never happened with my 617na. I'm assuming what you explained is the reason.

Still does help on cold starts imo you just gotta be careful.

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Doesn't seem to carry any more liabilities than the factory high-idle knob on a non-turbo car, as far as runaway RPM while unattended. I like it!

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'82 300CD
"Pearl", the very first turbo diesel 123 coupe
Totaled 11/23/18, rebuild in progress.
'85 300TD, "Artemis".
'78 300D euro, "Ol' Red", mostly retired.
'85 300D, "Gandalf".

It does because the pumps are not adjusted the same.

Ya, unfortunetly it's completely diff than the one on the non turbo. Non turbo knob I had now problem turning all the way up and walking away.

But this one, if you go past a certain point in the throttle it will sound fine one second and u come back few mins later and the engine is running at damn near full bore haha.

you can still make it work, it just takes some touch.

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In any event, kudos to you for the initiative !!

Thanks for sharing.

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1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

thanks it was just a fun cheap tinker project to get me back excited to work on my cars.

since this I've done sls delete with new springs and shocks. sold my old sls parts, bought a new (to me) 722.315 trans to swap out with my current 722.4.

currently swapping out seals, k1 and k2 pistons and springs on it before I throw it into the car

also welding up a new exhaust system tomorrow.

so I'm rolling right now it's really fun learning all these new things.

end goal is a hx35 and a superpump. we will see if I make it there!

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