Secondary Idle Adjustment? - Dodge Cummins Diesel Forum
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post #1 of 30 (permalink) Old 03-04-2019, 06:10 PM Thread Starter
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Secondary Idle Adjustment?

I've read up on the posts about adjusting the motor's idle using the throttle linkage rod, but what else can be done beyond this?

I've maxed out the length of my linkage on both ends (threaded rod almost unscrewed from the female ends), but my idle is still on the low side, right about at 500 in Drive w/ A/C on. Want to get it up to about 650 here as it's hard starting at the current level.

When I installed my new p-pump, I recall there was a plate on the side of it towards the back of the pump where the linkage connects. Can this be adjusted too? It looked like it was possible to change the angle of it, thus taking up some of the slack in the linkage. Now that's it's installed in the truck facing downwards, it's hard to see much.

What's even more bizarre, my linkage rod was capable of conventional idle adjustments right after I installed my new pump. The truck at first idled too high, so I backed it off quite a bit. Now I need to increase it, but the linkage is all maxed out. Any ideas what caused this?


'97 2500 Laramie 4x4, 60-lb Valve Springs, 4K GSK, PDD Stage 3 P-Pump, MBRP 5" Exhaust, PDD AFC Live, Built 47RE, Thuren 2" Coils, Bilstein 5100, Synergy track bar, RedHead Steering Gear
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post #2 of 30 (permalink) Old 03-04-2019, 07:13 PM
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Secondary Idle Adjustment?

You shouldn’t adjust your linkage. If you follow it all the way to the rear of the pump, it all rests on a cap screw. There’s a jam nut on the underside you loosen and then spin the cap screw up to increase throttle. 10mm I believe.


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post #3 of 30 (permalink) Old 03-04-2019, 07:48 PM
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Ooofff you should of left that alone. That rod is not meant to adjust idle. It is used to make sure the TPS, TV, and cruise control are all in proper alignment. There is only +-1mm adjustment allowed there and that is used for TPS adjustment.

The proper way to adjust idle is at the low idle stop on the pump.

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Originally Posted by SFGiants View Post
I've read up on the posts about adjusting the motor's idle using the throttle linkage rod, but what else can be done beyond this?

I've maxed out the length of my linkage on both ends (threaded rod almost unscrewed from the female ends), but my idle is still on the low side, right about at 500 in Drive w/ A/C on. Want to get it up to about 650 here as it's hard starting at the current level.

When I installed my new p-pump, I recall there was a plate on the side of it towards the back of the pump where the linkage connects. Can this be adjusted too? It looked like it was possible to change the angle of it, thus taking up some of the slack in the linkage. Now that's it's installed in the truck facing downwards, it's hard to see much.

What's even more bizarre, my linkage rod was capable of conventional idle adjustments right after I installed my new pump. The truck at first idled too high, so I backed it off quite a bit. Now I need to increase it, but the linkage is all maxed out. Any ideas what caused this?

91.0 D250 A727 w/ 216k on the clock. i/p replaced 20k ago, lift pump 2k, 1 turn fuel, 2 turns smoke, ground & polished AFC pin, timing bump, 366 spring 94 2500 4x4, 49k miles, Farrell Diesel rebuilt 215 pump, PDD 5x12 SAC, SXE 362, built 47RH
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post #4 of 30 (permalink) Old 03-04-2019, 08:44 PM Thread Starter
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Gosh darnit.

Ok, thanks guys. I'll give that a try. Hopefully the linkage isn't too messed up. I'll try to reset it towards somewhere in the middle for now.
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post #5 of 30 (permalink) Old 03-04-2019, 10:26 PM
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I suggest you open the factory service manual and adjust both the linkage rod and the idle by the book. Not much point in having a correct tool if you don't use it.

97 3500, 2 WD, G56, slightly bombed, 1.3 million miles with un-additized diesel fuel. Started the second million on 8/24/13
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post #6 of 30 (permalink) Old 03-04-2019, 11:51 PM Thread Starter
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Do you guys back off the locknut a ways down the screw, and then turn the screw by hand from its tip underneath? I'm having a heck of a time getting two 10mm wrenches down there.

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post #7 of 30 (permalink) Old 03-04-2019, 11:54 PM
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Yes, get it about where you want it and then tighten the lock nut. The idle will adjust up or down (Cant remember) a little when you tighten it down.

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post #8 of 30 (permalink) Old 03-05-2019, 01:36 AM
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Hope you’re taking GAmes advice on the manual and setting your linkage by the book. You can take the tranny out in short order with the wrong settings.

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post #9 of 30 (permalink) Old 03-05-2019, 01:59 AM Thread Starter
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Hope you’re taking GAmes advice on the manual and setting your linkage by the book. You can take the tranny out in short order with the wrong settings.
Yes, I'm going to address this tomorrow. And goodness, I did not realize it was that critical. I appreciate the warning.

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post #10 of 30 (permalink) Old 03-06-2019, 07:21 PM
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Quote:
Originally Posted by SFGiants View Post
Do you guys back off the locknut a ways down the screw, and then turn the screw by hand from its tip underneath? I'm having a heck of a time getting two 10mm wrenches down there.
It isn't in the easiest place to get to, but using a 10mm wrench from the top is how I do it. Having a helper to hold the throttle full forward would make it a bit easier. The bolt goes up to increase idle. A little bit of adjustment goes a long way.

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post #11 of 30 (permalink) Old 03-06-2019, 07:28 PM
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Part of the finickiness is the tendency of the throttle arm to wear a crater into the head of the bolt. I took mine out and recrowned it in the lathe, very easy to get it dialed in now.

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post #12 of 30 (permalink) Old 03-06-2019, 09:07 PM Thread Starter
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Quote:
Originally Posted by GAmes View Post
It isn't in the easiest place to get to, but using a 10mm wrench from the top is how I do it. Having a helper to hold the throttle full forward would make it a bit easier. The bolt goes up to increase idle. A little bit of adjustment goes a long way.
Thank you for the details, sir.

I was fighting like hell trying to get both hands down there AND be able to see the low idle screw at the same time. As soon as I gave up on seeing what I was doing and went by feel, it actually wasn't too bad. A 10mm ratcheting wrench on the bottom to loosen/tighten the nut relatively easily and a stubby on the bolt did the trick.

Regarding the throttle linkage, I was within an 1/8" of the 5 inch spec and figured it was close enough to drive to the shop today for my valve spring install, however, I'm going to go back in there tonight and get it perfect. Ended up adjusting the idle too high yesterday too, I did it with a cold motor and didn't compensate well for how it increases once warm.

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