Help! I don’t Get It!, Idle went out the window... Options

[MikeInMunich]

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

[VaccaRabite]

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