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Posted by: MikeInMunich Jul 22 2019, 08:34 AM

Everything was fine, until the last time I took my 1973 2.0 D-jettronic out...

First, Idle at 1600 when warm...thought the AAR valve was stuck open.

Turned off car. When I statierten it again the idle was perfect at 800, until I touched the gas pedal. Then it was almost 3000 and wouldn’t go back down unless I turned the car off. When doing so, same thing. Perfect idle until touching the gas pedal again.

Then it got worse. Went up to 4000, and eventually, worse, in that it was right there at 4000 again even if I turned the engine off and back on. Then it seemed to be only if the car was in neutral and not under load, but that was inconsistent.

So I reckoned it was a vacuum leak but couldn’t see any tubes with issues. Then I was thinking that the clutch cable an accelerator cable were conflicting, but that’s not been a problem before for me and it would explain how the engine would idle at 800 again by turning off the engine and then starting the car again.

So, what do ya reckon the issue is?

Thanks for your help!

Mike in Munich

Posted by: PanelBilly Jul 22 2019, 08:41 AM

Cable is binding?

Posted by: 76-914 Jul 22 2019, 12:07 PM

I wondering what could have that much influence over the idle speed other than the cable or throttle body/butterfly binding.

Posted by: dr914@autoatlanta.com Jul 22 2019, 12:39 PM

I agree with the other two replies, acc cable sticking. On the outside chance it is not, the decel valve is sticking

Posted by: MikeInMunich Jul 22 2019, 01:03 PM

Thanks gentlemen. I shall update...

Posted by: Dave_Darling Jul 22 2019, 04:59 PM

Could also be a big air leak. As in, one of the larger hoses has popped off the manifold.

--DD

Posted by: MikeInMunich Jul 22 2019, 10:55 PM

Thanks Dave. Question...what does / might it tell us, that turning the car off and back on again had enabled the idle to return to normal until I touched the gas pedal again? Only very slightly touching it would trigger the idle to go back up very high...and eventually, while driving home a few miles with the problem, turning it off and back on again ceased to help / „reset“ the idle, while it also wasn’t racing at 3000 anymore rather had increased to 4000 before I made it home.

I had checked all the hoses and didn’t see anything.

If the accelerator cable was stuck, why would the idle go back down after turning the car off? Here I must admit that I have the habit of stepping on the clutch (but not the gas pedal) when starting the car.

What do you think about George‘s suggestion that it could be the decel valve?

Thanks for your time!

M.i.M.

Posted by: VaccaRabite Jul 23 2019, 06:43 AM

Well, its clear that you have an air leak.

So either the throttle is sticking, which is easy to test. Just wait till the engine spins up to a 4K idle and reach into the engine bay and see if you can manually close the throttle (or just pull on the throttle pedal with your foot and see what happens).

If nothing happens, you know you have eliminated the Acc cable and throttle body.

While you have the engine lid open, look for air lines that have come loose. Should be somewhat obvious if you have a hose barb open. Could be less obvious if you have a split air hose somewhere.

If its not either of the above, start looking at all the things that are alternative sources of air going into the engine. AAR, Decel, etc.

It does not take much of a leak to get a 3K idle. You would be surprised.

Zach

Posted by: MikeInMunich Aug 7 2019, 01:32 PM

It was a vacuum leak. Fixed.