'76 Beetle High Idle at Cold Start <35F

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JRR
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'76 Beetle High Idle at Cold Start <35F

Post by JRR » Mon Apr 29, 2019 11:45 am

Hello,

I have a new to me '76 FI Beetle that idles very high at cold start when temp is low. Idle seems to step down "normally" after a "nominal" period of time. AFAIK.

The vacuum hoses are new and thermostat and flaps are present.

Is this normal, or if not, where should I start troubleshooting? Temp sensors or Auxiliary Air Regulator?

Thank you, this site is fantastic and the double relay info helped me wire the fuel pump back to factory operation. It was wired upon purchase to operate with key on. (Even I thought that carried too much immolative risk.)

JEff

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Re: '76 Beetle High Idle at Cold Start <35F

Post by asiab3 » Mon Apr 29, 2019 6:47 pm

Hi Jeff,

Does the car idle normally once warmed up? Any lumpiness or hesitations? It’s important to rule out vacuum leaks first. Also, high cold idle is fine, assuming you’re not hitting something crazy high like 2,000 RPM.

Assuming your intake tract is good... The auxiliary air regulator (AAR) is your fast idle mechanism during cold starts. Designed to help overcome cold engine friction, it has an inner heating element that closes a throttle bypass gate as the engine warms up and settles into its “regular” idle.

Diagnose the AAR as the culprit by pinching/cutting off airflow in the long braided hose that connects to the front right of the AAR and see if the cold idle drops. Drops? Read on.

On a fuel-injected bug, you can carefully remove the molded AAR hose that lives amidst the belt and pulleys and peek into the AAR. You might need a flashlight, but you should be able to see how open the gate is. Check it out cold, and fully warmed up (engine off.)

Once you’ve got a feel for how open it is at cold start/warmed up, you can take a 6mm wrench to a cold engine and loosen the hex nut on the AAR and allow the gate to close only slightly. Gently snug the nut (careful- easy to strip the stud) and check your work by starting the engine.

Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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Re: '76 Beetle High Idle at Cold Start <35F

Post by JRR » Tue Apr 30, 2019 3:58 am

Hello
Does the car idle normally once warmed up? Any lumpiness or hesitations? It’s important to rule out vacuum leaks first. Also, high cold idle is fine, assuming you’re not hitting something crazy high like 2,000 RPM.
Yes, it idles like a champ when warmed up. Or started at over 45-50F. And it went to crazy high for a minute then settled down. Yesterday was the first cold morning I have experienced with it. Will diagnose and get back.

Thanks very much

Jeff

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Re: '76 Beetle High Idle at Cold Start <35F

Post by JRR » Tue Apr 30, 2019 6:40 pm

Hello, Clamping the hose to intake did bring the idle down to acceptable rpm. Proceeding to the AAR adjustment. I removed the AAR so I could see what I was doing. Loosening the nut did not result in any change in the aperture. I'm not sure what I am adjusting with that nut....(I saw the open AAR on the Samba. Am I interfering with the spring loaded plate or closing the static elliptical orifice?) Below is as closed in the cold position as I could get the plate:[image]https://photos.app.goo.gl/Row2V2zCLeTa8a3fA[/image]

I hit both ends with penetrating oil and reintalled. The first start was high idle, but not as riduclulsly high as before. Kind of defeated, something does not seem right. Left it alone for couple hours. Returned and started, idle was acceptable, then decreased to just below where it was before this issue started. (Sorry I did not mention that this was a relatively new issue in my brief ownership.) May be a bit too low, as coming off a throttle stab, the revs would go low enough to light the gen light and give me the half-second of questioning if the engine died before igniting the next cylinder. I think that it would be normal to slightly adjust the idle screw after adjusting the AAR to

I'll check tomorrow morning to see if it holds. I'll post what happens. Continuing thanks for your guidance.

Jeff

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Re: '76 Beetle High Idle at Cold Start <35F

Post by JRR » Wed May 01, 2019 4:32 am

Working well this morning. Thanks again. Jeff

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Re: '76 Beetle High Idle at Cold Start <35F

Post by Amskeptic » Wed May 01, 2019 9:54 am

JRR wrote:
Wed May 01, 2019 4:32 am
Working well this morning. Thanks again. Jeff
Jeff, you do not get to leave just yet. The adjusting nut on the AAR is actually a sliding anchor/lever for the rotating gate valve inside. When you loosen the 8mm locknut, the screw can then slide and execute your adjustment.
Glad it is working well this morning.
And a toast to those who care about immolative risks.
Colin
BobD - 78 Bus . . . 112,660 miles
Chloe - 70 bus . . . 206,845 miles
Naranja - 77 Westy . . . 121,400 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 91 Lexus LS400 . . . 92,435 miles

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Re: '76 Beetle High Idle at Cold Start <35F

Post by JRR » Wed May 01, 2019 11:01 am

Thanks Colin, so the adjustment is not rotational, but the small distance side to side? I see...My reference was the electric Solex chokes. I'm still cold idling higher than I like, but seem to be at the extent of adjustment. Is this a normal cold AAR opening size? https://photos.app.goo.gl/5Tdnvn7pbDmwr8KC6 (Sorry, a forum kung-fu grasshopper)

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Re: '76 Beetle High Idle at Cold Start <35F

Post by JRR » Wed May 01, 2019 11:08 am

Crap nevermind, per Robbie "This adjustment is *not* about rotating the screw and watching the aperture open. It actually sort of slides around, so jam that allen wrench to get the aperture as open as you can..."

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Re: '76 Beetle High Idle at Cold Start <35F

Post by JRR » Wed May 01, 2019 11:17 am

Double nevermind, Per Robbie's quote of Colin.

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Re: '76 Beetle High Idle at Cold Start <35F

Post by asiab3 » Thu May 02, 2019 12:46 am

While I can’t see the photo, there is no “normal.” New engines are tighter and need more opening. Same with high elevation operation where oxygen is rarer. Same with cooler environments with thicker oil. The opposite is true for older and looser engines.

So, like, just get it where your car likes it and don’t stress about it? :)
Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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Re: '76 Beetle High Idle at Cold Start <35F

Post by JRR » Thu May 02, 2019 4:22 am

Got it. Thanks much.

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Re: '76 Beetle High Idle at Cold Start <35F

Post by JRR » Tue May 07, 2019 5:47 pm

Hello again,

Found that the bimetal assembly is rotating inside the housing. Is there a more elegant way, than a hose clamp, to hold the plastic end fast?

Thanks

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Re: '76 Beetle High Idle at Cold Start <35F

Post by asiab3 » Tue May 07, 2019 7:02 pm

I'm not sure what you mean by "plastic end." Can you elaborate what and why?

NOTE! That some bugs came with dual vacuum dual advance (DVDA) distributors that retarded the idle timing to around 5°ATDC, and modified the airflow compared to cars without the extra vacuum retard (SVDA,) which idled at 7.5°BTDC. If an AAR for a DVDA engine is installed on an SVDA engine, the cold idle will be fast indeed, as the SVDA engine is more efficient at idle.

Unrelated, here is a picture of a '78 project I have right now. The AAR is open this far on a 60°f morning, and I am pleased with the cold idle. We HAVE a vacuum retard, with idle timing clocking in at 5°ATDC, hoses on. What about you?

Robbie

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1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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Re: '76 Beetle High Idle at Cold Start <35F

Post by JRR » Wed May 08, 2019 3:50 am

Hello Robbie,

I meant the 12VDC connector will rotate in the steel housing. I can see and feel the bi-metal tab engage and move the sprung cover plate as I hand rotate the connector. Using at hose clamp to bind the electrical connector to the steel housing.

Played with the AAR, 12VDC PS, and the freezer last night. Set the opening to approx 1/2 your example at full cold. Installed it this morning and took two starts to get to idle. Will adjust again. I think I'm gettng closer.

I do have a DVDA. I believe it is the original distributor. Will time it again this afternoon. Not familiar with them, had the SVDA on the old bug.

Thanks for your help, I think I'm getting closer.

Jeff

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Re: '76 Beetle High Idle at Cold Start <35F

Post by Amskeptic » Wed May 08, 2019 7:06 am

JRR wrote:
Wed May 08, 2019 3:50 am
Hello Robbie,
I meant the 12VDC connector will rotate in the steel housing.
Jeff
That pot-metal crap doesn't get to be called "steel".
You are lucky to have this nifty adjustability feature but you must stop that rotational ability once you have it clocked acceptably. It is normally crimped. I would do three equidistant epoxy drops at the parting line/seam, so I could break it loose if I wanted to in the future. Do not adjust to taste. Adjust so that it is CLOSED after four minutes of 12 volts.
Colin
BobD - 78 Bus . . . 112,660 miles
Chloe - 70 bus . . . 206,845 miles
Naranja - 77 Westy . . . 121,400 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 91 Lexus LS400 . . . 92,435 miles

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