'74 914 2.0 timing/ idle issue

[duffy 911]

Thanks in advance for any pointers. If I set the timing to spec(27*btdc @3500rpm) I can't get the idle below 2000, air bypass screw closed.
Vacuum hoses disconnected and plugged.
Vehicle is equipped with Petronix type ignition.
I wonder if manifold pressure sensor can have this effect? Any thoughts appreciated.
Duffy

[Dave at Pelican Parts]

MPS generally won't cause these symptoms. What will cause it is some kind of air leak. Air is getting into the manifold somehow. For a 2000 RPM idle, the leak is probably decent sized. Check for any ports on the manifold that are not connected to anything, or hoses that are disconnected. Also make sure you have no hoses directly from the air cleaner to the manifold--there should always be some kind of component (e.g., aux air regulator, decel valve) in the way.

Finally, make sure that the AAR and the DV are closed in normal operation. When the AAR is warmed up or the engine has been runing for ~10 minutes, you shouldn't be able to blow much if any air through it. The DV should not allow air through except when very high vacuum is pulled on the small hose leading to it.

--DD

[duffy 911]

Thanks Dave. Armed with your suggestions I will smoke test it again and specifically look at AAR and DV for internal leakage. Minor throttle shaft leakage noted initially.
Duffy

[duffy 911]

For the record....AAR was the culprit!
Thanks Dave.