Fast Idle issue

Engine, transmission, rear-end, driveline, etc..

Fast Idle issue

Postby fosterfarm » Mon Dec 04, 2017 8:46 pm

I have a 440 (from a 70' Chrysler Imperial) w/ an Edelbrock carb and a 4spd in my D200. It starts up good and idles around 400rpm. Once I start driving and then come to a stop, the idle stays fast at around 1100-1200rpm until I tap the gas, and then it settles back down to 400rpm. Any ideas on what could be causing this?

Thanks ahead of time!
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Re: Fast Idle issue

Postby 12Valve » Mon Dec 04, 2017 9:17 pm

Sounds like the throttle is getting hung up in the carb, possibly the butterfly valve getting stuck, check your throttle return spring for excessive slack. One of the Weber DCOE 40's in my dads BMW 2002 has that issue, idles fast whack the throttle idle dies down to normal.
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Re: Fast Idle issue

Postby dodgeboykim » Mon Dec 04, 2017 10:35 pm

12Valve wrote:Sounds like the throttle is getting hung up in the carb, possibly the butterfly valve getting stuck, check your throttle return spring for excessive slack. One of the Weber DCOE 40's in my dads BMW 2002 has that issue, idles fast whack the throttle idle dies down to normal.



400 Idle rpm is too low. You must have some linkage binding or throttle plate hitting or its flipping to high idle cam.
My truck is younger than me.
66 W100. 70 D 500 with 69 Hiab Speed Loader. 96 Ram 3500 Club Cab Cummin's 5 spd. 97 Ram 1500 Club Cab 5.9 gas auto. 83 W200 L/B 360 auto on propane.
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Re: Fast Idle issue

Postby fosterfarm » Mon Dec 04, 2017 11:37 pm

dodgeboykim wrote:400 Idle rpm is too low. You must have some linkage binding or throttle plate hitting or its flipping to high idle cam.


Apologies, I misread the tach. It's 1000rpm when idling correctly and it gets stuck at 2000rpm.
Linkage all looks good - spring seems fine. nothing is catching or binding when I'm revving - just seems to remain high after i've shifted through some gears and then go into neutral. From my reading it seems that this behavior is indicative of a vacuum leak. Time to check the hoses.
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Re: Fast Idle issue

Postby 12Valve » Tue Dec 05, 2017 1:17 am

It could be a vacuum leak however that would be also prevalent during idle even after the car is warmed up. Does the engine hunt in Rpms?
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Re: Fast Idle issue

Postby MadMC63 » Tue Dec 05, 2017 6:58 am

You have an Edlebrock carb with electric or manual choke?
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Re: Fast Idle issue

Postby 12Valve » Tue Dec 05, 2017 8:45 pm

Also to find a vacuum leak use some combustible spray like carb cleaner, brake cleaner or something of the sort. spray around the base of the carb as well as the intake manifold. If you have a vacuum leak the rpm will increase then slowly back down to normal
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Re: Fast Idle issue

Postby fosterfarm » Thu Dec 07, 2017 1:35 am

MadMC63 wrote:You have an Edlebrock carb with electric or manual choke?


Manual choke.
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Re: Fast Idle issue

Postby fosterfarm » Sun Dec 10, 2017 11:44 pm

Took some more time today to tinker with the intake and try and resolve the issue. See the photo below:
Intake.jpeg

It idles fine around 1000 RPM and when I tap the accelerator it returns to normal. If I hold the accelerator for any time (2 seconds or more) the throttle gets stuck open and it looks like the valve that i've outlined in red above is the part that is sticking. What causes this to stick? Any recommendations?
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Re: Fast Idle issue

Postby MadMC63 » Mon Dec 11, 2017 6:49 am

I think I would have a serious look at your linkages and cables, it all looks buggered up. Your accelerator cable vanishes behind the carb toward the right side of the engine and the kick-down linkage looks rigged too. The piece you have outlined is just a vent cover. Your accelerator cable should be attached to a bracket mounted at the rear of the intake manifold on the left side (which doesn't appear to be there) and the kick-down linkage should be attached similarly, plus there should be a spring pulling the kick-down linkage forward toward the carb and the throttle cable stud (where the stuff attaches to the carb) should be longer sticking out enough for the kick-down linkage and spring. Even the throttle return springs doesn't look right.

Throttle linkage stud.jpg
Throttle linkage stud.jpg (10.5 KiB) Viewed 124 times


Excellorator cable on the left and kick-down linkage on the right.
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Re: Fast Idle issue

Postby MadMC63 » Mon Dec 11, 2017 7:11 am

I'll go on record as saying the accelerator cable is the culprit due to length and alignment. It probably has moisture damage where it drops down behind the intake. If you disconnect the accelerator cable at the carb and, using your fingers, slide it back and forth to see if you can feel a rough spot. You'll need to do this slowly and it probably wouldn't hurt to disconnect the cable on the pedal side as well of course if I'm right a heavier return spring would be the quickest remedy.

Shouldn't it be more like this?
440-engine-details-throttle-return-spring.jpg
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Re: Fast Idle issue

Postby fosterfarm » Mon Dec 11, 2017 12:51 pm

MadMC63 wrote:I'll go on record as saying the accelerator cable is the culprit due to length and alignment. It probably has moisture damage where it drops down behind the intake. If you disconnect the accelerator cable at the carb and, using your fingers, slide it back and forth to see if you can feel a rough spot. You'll need to do this slowly and it probably wouldn't hurt to disconnect the cable on the pedal side as well of course if I'm right a heavier return spring would be the quickest remedy.

Shouldn't it be more like this?
440-engine-details-throttle-return-spring.jpg


I guess it should! The joys of having a franken-engine. Any suggestions on where I find these parts?
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Re: Fast Idle issue

Postby fosterfarm » Mon Dec 11, 2017 8:00 pm

So looking at the accelerator linkage for Sweptlines, they aren't like the 440 photo above (that appears to be from a charger).
Here's the original D200 linkage (which is what mine looks like): http://www.sweptline.org/fuel63_68/14-07.gif
Do I need to change out the whole linkage???
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Re: Fast Idle issue

Postby my5thmopar » Mon Dec 11, 2017 8:42 pm

I thought I read that the truck has a manual trans???? That setup looks like a early rod style with a AT kick down on it. So there shouldn't be a cable? I can't tell what you have from the picture. The PCV isn't hooked up in the pix but, I'm guessing normally it is. You probably you just get a Lokar and be done with it or one of the guys will have the setup from a parts truck. Put an ad in the parts wanted section. That spring looks way too light
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Re: Fast Idle issue

Postby MadMC63 » Mon Dec 11, 2017 9:20 pm

O.K. when I saw the picture I forgot everything I read and concentrated on what I did and did not see. If you have a manual trans you don't have a kick-down linkage but you do have a kick-down linkage piece in your setup and its upside down in order for it to work. I'm guessing the original rod was to short or lost so they grabbed the first thing they could find to get it going and you are the lucky recipient of "awh hell at's good". Just disconnect the throttle linkage, crank the truck and use your hand to move the throttle. Hold it an the rpm you think you run when the problem occurs release it and see if you still have the problem. If the problem goes away the linkage is the problem if not look at the return maybe its weak. Try without both and see if you can feel the throttle shaft binding. Is the intergrated spring on the opposite side of the throttle shaft broken?
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Re: Fast Idle issue

Postby fosterfarm » Wed Dec 13, 2017 12:14 pm

Inspected and every part of the carb seems to be working as it should (springs etc.).
My current thinking is to just get a new throttle rod to replace the kick-down piece... however, I noticed that pulling the throttle linkage back to the firewall only opens the throttle about half way. Is this normal? (see photos) Seems like I needs progressive linkage for full engagement.
ThrottleRod1.jpg

ThrottleRod2.jpg

ThrottleRod3.jpg
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Re: Fast Idle issue

Postby MadMC63 » Wed Dec 13, 2017 2:40 pm

Been awhile since I messed with one of those. Any throttle linkage, be it a rod or cable, should open the the butterfly's fully at wide open throttle and allow the butterfly to close properly when released. I saw a truck on eBay with a six in it and it had the same bend in the accelerator rod. Made me rethink the kick-down rod idea but the end at the carb is definitlly a kick-down piece. My thought was when you accelerate all the linkage pulls like it should but, when you relaese the throttle the washer catches on the slot just before the end keeeping the carb from fully returning to idle and when you tap the throttle it allows it to seat completely like it should and the engine idles down to normal.
Much better pictures OBTW. These don't make the return spring look so out-of-wack and provide a much better veiw of everything.
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Re: Fast Idle issue

Postby MadMC63 » Wed Dec 13, 2017 4:14 pm

This is what I had seen on eBay.

1966 D100.jpg
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Re: Fast Idle issue

Postby fosterfarm » Wed Dec 13, 2017 4:53 pm

MadMC63 wrote:Any throttle linkage, be it a rod or cable, should open the the butterfly's fully at wide open throttle and allow the butterfly to close properly when released.


So this is what concerns me - if you look at the last picture I posted, the throttle linkage is as far as it’ll go (pedal to the floor). But actual throttle/butterflies are only about half. In the picture I’m pushing the throttle lever on the carb forward and goes another inch at least. Seems like I’m missing some lever to increase the pull length at the carb.
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Re: Fast Idle issue

Postby MadMC63 » Wed Dec 13, 2017 7:35 pm

On the end attached to the carb I think the regular end srews in and out to accomplish some adjustment and I know the kick-down end works that way so is there any adjustment left or is it screwed on the rod as far as it can go? It could be the original end was to short, didn't work, and the adapted piece is to long but worked well enough to be drivable. I know that six from eBay looked like yours so maybe your truck was originaly a six instead of a V8 so the rod from the firewall bracket was just to short.
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