MFI idle Question

[steve meltzer]

I have a '69 911E with a 73-T MFI motor. About six weeks ago, I first noted that the car idles normally at about 1100 at start up, but once full warmed up and driving the idle stays at about 1800 when you come to a stop. It's not perfectly consistent, but it's pretty consistent behavior. It never happens when it's cold and only happens when it's fully warmed up. Like I say, it then occurs about 90% of the time. The other 10% of the time, the idle returns to 1K, or thereabouts like it should. The car runs great otherwise. I believe this is an MFI problem and not electrical. comments? (I do plan to check for vacuum leaks in the next day or two.) thanx steve

[dreichman]

I had a very similar problem. Turns out my spark advance in the distributor was gummed up. It would not rotate back to the idle position. I cleaned it up and all was good. A thousand miles or so later and it’s still idling properly. Hope this helps.

[356RS]

Originally Posted by dreichman

I had a very similar problem. Turns out my spark advance in the distributor was gummed up.

I agree 100%. Really nothing in the MFI pump that can all of a sudden raise the idle speed. Tight linkage heating up or the distributer advance.

[Jonny042]

Originally Posted by 356RS

I agree 100%. Really nothing in the MFI pump that can all of a sudden raise the idle speed. Tight linkage heating up or the distributer advance.

Maybe the zero throttle switch if it's still installed?

[cmcfaul]

Assuming the throttle level it pushed all the way down

[tobluforu]

When this happens, does moving the throttle linkage rod/deflector/cross bar shaft, or whatever you want to call it, forward, decrease idle?

[Neven911]

The idle will increase as the engine warms and the MFI leans out, having said that the distributors on the 73 MFI have vacuum retard not advance so the idle will drop back (due to the retard) as the vacuum builds in the distributor (this give it a rather unstable behaviour), so I would check your distributor, with a timing light you should see the retard in action (esp. if you suck on the pipe), could be for example that the throttle plate on the inlet that feeds this is sealing intermittently and not generating a vacuum