RPMs very slow to drop Options

[Tdskip]

Hi guys-hoping to get some sage advice here on what's going on. I am picking at the 1973 1.7 L D-jet car and when I was test driving her today she did not want to return back to idle.

When you accelerate in first gear up to about 3500 or 4000 RPM and then take your foot off the gas the RPMs stay at the same level or climb slightly and then only slowly drift down.

She starts fine and will idle at about 1000 RPM, air bleed screw is close to all the way in.

There is an aftermarket return spring on the throttle assembly but appears to have the right amount of tension. I took the air cleaner off and when I manually actually the throttle it appears to settle down faster than when I do it with the gas pedal.

The pedal does not appear to be binding on the carpet or interior trim.

Any ideas for me?

Thanks!

[Dave_Darling]

Suspects:
- Air leaks. This includes the possibility that the throttle plate isn't closing correctly. Or that the decel valve is hanging open. Or some other air leak.
- Timing. Advanced timing will raise your idle; if the timing sticks advanced it will keep the RPMs up, then when the timing drops so will the RPMs.

--DD

[Tdskip]

Suspects:
- Air leaks. This includes the possibility that the throttle plate isn't closing correctly. Or that the decel valve is hanging open. Or some other air leak.
- Timing. Advanced timing will raise your idle; if the timing sticks advanced it will keep the RPMs up, then when the timing drops so will the RPMs.

--DD

First, thanks to all for the ideas.

Dave - I did find that when I was operating the throttle by hand at one point it seemed to close (but with RPMs still too high) but then it further "snapped" back to closed.

Is there a lip or ridge in there that gets worn or gunked up?

I'll try disconnecting the accelerator pedal and then cable to see if that makes a difference.

Thanks!

[Dave_Darling]

Is there a lip or ridge in [the throttle body] that gets worn or gunked up?

There wasn't one when the throttle body was new. There may be one now... The shaft may also have worn the bore that it rides in out of round. And there could be other potential issues that cause that behavior.

Start isolating things. Disconnecting the throttle pedal will remove that from the equation. If you still have sticking, disconnect the throttle cable at the throttle body end. If you still have sticking, the problem is in the throttle body assembly.

--DD